Car Battery Drains Overnight
My wife drives a Honda Accord. Great little car. Still runs great. It has one serious problem which it has had for several years now.
The battery rapidly drains when the car sits for a couple of days. I replaced the alternator and battery each more than once to no avail. I used an amp meter to check drains on various cables while removing fuses and relays, one at a time.
I discovered a drain going to the alternator on a cable that is supposed to provide current to the battery when the alternator is spinning.
I figured the alternator diodes were going bad. Why they kept blowing on new alternators I couldn’t figure out.
I bought a couple of high-amperage, high-voltage diodes and put them in-line on the alternator cable.
The idea was to replace the functionality of the bad alternator diodes and prevent current from draining back through the alternator.
It didn’t help but it didn’t hurt either. They’re still in-line and the car runs fine. The only thing I could find that would stop the battery from completely draining was a device called a “battery brain”. Battery Brain.com It monitors battery voltage and disconnects the battery before it gets too low.
There is a key-chain wireless module with a button you press to connect the battery when you want to star the car. Works pretty well.
I noticed one other thing about the car. When I’ve been in the garage I’ve heard a buzzing noise from the Honda’s engine compartment. Checking under the hood indicated the noise was coming from the fuse box.
Opening that, I discovered it was coming from a relay which controls the radiator fans. I think I may have replaced that relay once before but am not sure.
Any thoughts?
Hi there Gregg,
You are on the right track, just keep investigating. I am not sure what you see as a drain going to the alternator, or if that is really a drain at all, but the buzzing noise under the hood is definitely going to be a drain on the electrical system and something you should keep investigating.
An electrical “drain” can be anything that is drawing power (draining) from the battery with the engine/key OFF. Every vehicle will have some amount of electrical drain which is normal. Radio and clock memory and engine computer memory will drain a small amount of battery power with the key off, and that is normal.
Again I am not real sure what the buzzing noise could be coming from, but any electrical noise/buzz/vibration etc. should not be there, and is probably the source of your problem.
If you had told me the battery drains down while the engine is running, I would suspect a problem with the battery or the alternator, but I think you have already ruled them out.
If you get stuck trying to locate the drain I would take the vehicle to the dealership or a qualified electrical repair shop in your area and at least pay them to track down the source of the drain for you. You can always perform the repair yourself to save some money once you know what it is.
Tracking down an electrical drain can sometimes take hours! Make sure the shop you choose to help you has a qualified electrical mechanic so you don’t needlessly pay for inaccurate diagnosis time.
Some causes for an electrical drain
1. Trunk, hood, or interior light or glove box light that is staying on when the engine is OFF
2. Aftermarket radios, CD players, amplifiers, cell phone chargers etc. etc. are notorious for drains
3. Electric seat motors and electric antennae motors that are stuck in the ON position
4. Relays or components under the hood that are ON or running with the engine OFF – for instance electric cooling fan motors, anti lock brake pump motors, air ride suspension pump motors.
Thanks for the link to the batterybrain.com to help determine why a car battery drains overnight, I was unaware of it until now.
Please share this with your friends,
Austin Davis
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2003 Corolla Battery overnight Drain
I changed a new battery three years ago (warranty for 60 months)with No starting problem so far until I got an A/C recharging done at an auto repair shop two days ago. At the time of Freon recharging, the mechanic replaced a new relay at the fuse box in the engine compartment (as he said the old relay was”bad”). Unfortunately my car could not start this morning even No lights on the dashboard either. The battery drain was almost 100%. After a jump-start,the engine was running well. What did cause the battery drain so bad? Is the new relay wrong? Please advice.
So sorry for my delay, just swamped with questions lately. I would probably bet on a weak battery that is due for replacement. Not real sure what relay that was replaced, but probably not the cause of you problems. Weak battery, dirty or loose battery cables or an alternator that is not properly recharging the battery are the top 3 things I would check first.
Great site!
Our 2008 Honda Accord had new Bosch battery installed at 2:00 pm yesterday after very cold night, I went to start it and it failed to start the engine without the use of a jumper. I ran it for about half hour, turned it off and failed to run again, same problem! What do you suggest. Thank you, Rock.
Thanks Rock! Well, I would get an electrical test done first, check all battery connections and cables to make sure they are tight and clean, check for a voltage drain and check the alternator output. Might be a bad alternator, or something draining power from the battery with the key off. An electrical system test should tell you that.
I have a Toyota Camry XLE and it is draining brand new battery overnight. We have started the car and disconnected the battery and it runs on alternator only. There is a clicking noise under the dash against the fire wall and it sounds like a relay. I believe with all my heart that one of the big black fuses is gone out or a relay has gone out and that is the source of the overnight drain. But I don’t know for sure.
These types of issues are very hard to diagnose on my end of this computer. I can really only advise that you read the article about battery drain sources and rule out what you can, but to be honest I would go to the dealer and get a diagnosis….which it cheaper than guessing at parts.
Hi, sorry there are a lot of typos in my question. I meant the only fuse to make the test light go down was labeled, l/h bec batt2. And the ac is not getting cool, but cycling on and off, you can hear it doing this under the hood.
Hi, don’t know if you still visit this site, but i too am having problems with something draining the battery on my 03 Chevy Malibu. If I drive the car daily won’t have the problem, if it sits one day no start, I need a jump. Most of the time I can go up to 2 weeks driving it daily, but soon I will need a jump. I stumbled upon this website looking for help. I had someone pull fuses with test light on the battery, the only fuse that made light go down sign if I can’t was a fuse labeled…. L/h bec batt 2….. he told me it was my left fuse block because when he unplugged it the light went down… Other mechanics told me it’s supposed to go down when unplugged because it’s fusing the car. Paid $80 for a mechanizing to look at the car and the only thing he told me was the door locks where bad, so he removed them, but it still has a draw somewhere, he also said he couldn’t read my computer with his machine which is a sign of a bad bcm, I’m trying to save up money to bring it to the dealership now, because they are expensive. Im so stressed out trying to find the problem. I have no help. Now my a/c is now blowing cool anymore. And it keeps cycling on and off, not staying on long enough to cool. Those are just some of the problems. I know I should get rid of it, but really can’t afford it… sorry for rambling, but if you get my question, PLEASE respond. Thanks in advance
First things first, replace the battery with a new one or a known good battery and see what happens. Also make sure the battery cable connections are clean and tight. Honestly, not real sure what the fuse is they removed, or if it is meaningful to your issue or not….kinda dont think it is. Hopefully you have a bad cell in the battery, and a new one will solve this issue.
The A/C issue, sounds like you are low on Freon gas, and that means you have a leak in the system somewhere that needs to be found and repaired. I would solve the battery issue first and see how much money you have left before looking into the A/C, which is probably not related to the battery.
Ok I have been looking for a website to help me. I have a 1992 Ford Taurus GO, the power windows, power locks and power seats do not work. About 6 months ago I had the windshield wipers fixed and ever since everything stopped working. I think maybe they unplugged something…idk. I checked all fuses inside and outside the car…any suggestions? And also the battery drains too.
Hummmm, first thing. Check the electric door locks and windows from another door other than the driver door to rule out an issue with the “master” door switch. If still nothing, I would check all the large fuses under the hood, then check for power coming from the battery to each of those fuses. You probably lost battery power somehow, so start at the battery and go to the under hood fuses then to the in car fuses. You will probably need a mechanic to help you, these things can be tricky and time consuming and you really need a wiring diagram and a multi meter tester to check for power.
I have a 09 Honda Accord. One morning I noticed the car bettery was dead, I replaced a new bettery, after few days the bettery was drain. Jump start it & it worked fine for few days & again the bettery was drain over night. What is the possible cause?
Please reply back with your answer.
Thanks!
I would get your alternator tested, and make darn sure your battery cables are CLEAN and tight! If those are fine, you need a “voltage drain test” which should be done on the car, so you would leave the car at the shop for a few hours with test equipment hooked up to locate where the drain is coming from…..aftermarket radio, electric seat stuck in ON position, glove or hood light staying on etc. etc.
I have a 96 ford mustang, this morning I cranked my car up and I keep hearing this buzzing noise that sounds like a belt with to much tension on it but I don’t believe its the belt because I hear the noise around my alternator.. any ideas?
It could be your alternator having an internal problem, or a bad belt tensioner pulley that is flopping around because it is worn out, or an a/c compressor pulley that has a problem. Sometimes the easiest thing to do is remove the belt, start engine and make sure noise is gone, then spin each of the pulleys by hand until you hear the noise and find the problem.
So i would also check out the alternator because of the voltage regulator on it. When a diode goes out on the voltage reg you will have a little energy vampire all the time as for the buzzing sorry i would have to look at the vehicle.
2006 Nissan Altima: battery drain problem.
The alternator has been changed. Battery tested good. Battery will charge but later die.
My question is will a broken key fob (got wet) cause a drain somehow?
It’s not a smart key. I can enter and start my car manually. But it did open/lock my doors and work with the car alarm. I’m wondering if somehow it’s related to the battery drain problem ( the fob and car alarm?)
Sorry for my delay Hollie. No, probably has nothing to do with the key fob, but COULD be an alarm issue. Anything that is left ON when the key is off is suspect of a battery drain, alarms, radios (clock and memory functions are ON 24/7) electric seats, dome-trunk-hood-glovebox lights, etc. etc.
Your mechanic needs to do a battery drain test to see how many AMPS are being sucked off the battery with the key off, then start unplugging items until they find the culprit. Removing fuses one at a time is the easiest and fastest way to do it yourself to at least rule things out and try and narrow down an area of interest. I.e. radio fuse, interior light fuse etc.
I have a 1999 VW Jetta VR6, somehow the battery gets drained over the course of 90 days or so. I’ve replaced the battery 3 times and had the alternator checked out by a mechanic. This last time it died, I gave a neighbor a jump the day before. When I went to start the car, it click but didn’t start. After a little while, I went back out to try again and once I tried to start it, i heard a clicking sound even after I had given up on trying to start. I would try to jump but don’t think it will help.
Hey Jeff
90 days? That is a little too long for a car to sit idle with the battery still hooked up. The engine computer, radio, alarm system etc. are still drawing battery power while the key is off.
I would get your mechanic to do an over night “voltage drain test” on your vehicle…not just the battery itself but hook up a voltmeter to the vehicle and leave it overnight and see what the amperage drain is.
You might have something that is sucking too much battery juice with the key off, or 90 days is just too long. A battery that is completely dead or has a bad internal cell might not jump start.
IF all else fails, you might want to try a different battery manufacture and battery size. Check with the dealer and see what they recommend for battery cold cranking amps, size etc. to make sure you are replacing it with a comparable battery.
I like to do a weight test when I buy a battery, pick up the battery and see how much it weighs compared to other brands. The heavier it is the more lead inside which should last longer. Some Walmart batteries (for example) are very light weight. A good battery should cost $100…not $49
Can a bad battery cause the drain? Silly question sorry.
There are no silly questions here, all of them are very good and valid to ask…YES a bad battery (a bad cell inside the battery) could be the cause of a battery that can not hold a charge for an extended period of time. My rule of thumb is a battery that is 4 years old should be replaced. You want to replace the battery before you HAVE to replace the battery…in a parking lot, in the rain, on a holiday at night with your family in the car. 🙂
My son replaced the radio in my car with a much louder one and ever since then my battery drains down if I dont drive the car each day. Related?
Yes, probably very much related. I would guess that either there is a problem with the installation of the radio or a problem with the radio itself. Some people add amplifiers to their car stereo’s and they suck a lot of juice from the battery. Make sure those items are on the proper fuse block so all power to them is shut off when the key is OFF.
Wow, never thought about my electric seat causing a battery drain. I think my kids must have been playing with the buttons because the seat motor was running non stop and drained my battery down. Thank you!
Yes, I have seen it happen a few times in my shop as well. You have to rule out everything 🙂
Awesome tips, thank you so much!
Yep, you are right I just had a bad connection at my battery. You saved me some cash today.
It is interesting to have a problem , do a search and find others have the same issue. Here is my story with theory. This just happened over the weekend of Dec 22nd 2012. I have a ’99 4Runner that has been problem free until now. Good car! But………I was surprised to have dead battery with no warning. I thought that was what all the idiot lights were for lol. Anyway, so I have this battery issue (I thought), and after having it ‘tested’ <a whole other issue regarding sub par service already addressed on Yelp BTH, I replaced the battery and THAT evening, the battery was dead again! Being somewhat knowledgeable, I realized I had a drain on the battery with the ignition off and it took at least 6 hours for this to occur. When I went to put a charge on the battery, I heard a clicking or what sounded like a recycling noise coming from somewhere near the fuses box under the hood. I had a helper and when I went to open the driver door to check to see if the ignition was off (it was), she told me the noise stopped! I closed the door and the noise started up again after a few seconds. We tried this several times with the same result. The only thing I can determine is it is related to the power door lock since it is an open circuit. I guess it's possible it could be something else but I cannot imagine what. The thing is, the problem went away so it is an intermittent problem. Power door locks are easy to replace so I will do that and let you all know the outcome up the road.
These kinds of battery drain issues can be a REAL pain to track down sometimes. Just start with the most obvious electrical stuff first and rule them out.
Electric seat motors stuck ON
Electric antennas in the fender constantly running
Electric windows (usually hear a buzzing noise inside door panel)
Tailgate lights, dome, glove box, hood, etc. etc.
To drain a new battery down in just hours, it must be a pretty big drain.
Engine computers
Main power relays
Internal voltage regulators inside the alternator (unplug harness connector at alternator overnight)
Body control computers
There should be a fuse for power door locks/windows etc. so I would remove the fuse first before replacing parts.
Keep us posted
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Hi I am experiencing the same problem I recently had a battery drain test by an electric shop I really did not trust they said the drain was coming from my driver door or power mirror which does not work can that be right
It is possible that either the mirror motor is causing the drain or something else inside the door like the door lock actuator motor or the window lift motor. They should be able to easily disconnect those items and see if the drain goes away to prove that is the cause.
A “drain” is any electrical device that is ON when it should be OFF, thus draining power from the battery when the vehicle is not running. When the engine is on the alternator and a strong battery can over come most drains, because the alternator is recharging the battery. There is always a small drain with the engine off like the onboard computer, the radio and clock, security system etc. These should be relatively small drains and a strong battery should over come them.
If your electric mirror does not work anyway, I would disconnect the electrical supply and see if the drain goes away. If it does not, you will need to investigate the drain further.
Common drains are:
1. Dome lights, trunk or hood or glove box lights ON
2. Electric seat motors that are ON (sometimes you can listen under the seat for a buzzing noise)
3. Aftermarket radios, TV’s or amplifiers
4. An internal problem inside the alternator
5. Electric radio antenna’s (usually you can hear a buzzing noise around them)
Drains are sometimes difficult to track down and can take a few hours….which can be expensive. Find a good shop with a knowledgeable mechanic.
OOPS! Big Typo! I didn’t mean to say we’ve ALWAYS had trouble even opening the door!
I meant to say, that recently, in the last 5 months, we have HAD trouble trying to get the car’s door on the driver’s side open, because obviously rain got into the door, inside it, and our mechanic look at it, and say rust inside the door!
Well, that makes sense, since it was pouring rain out, and the cop, literally insisted we keep our car’s windows rolled down to the bottom of the window, even though we pleaded with them to not do that to us!
Don’t come to southern New England…. it’s a mess in that state!
Hi there, so to understand your question better. Your battery is draining down over night as you let the car sit? I would do this, if this is the case.
2. Is the alternator charging the battery, check the output of the alternator
3. Is there a voltage drain somewhere…is something ON, when it should be off. Interior lights, glove box, trunk and hood lights, electric seat motors running etc. etc. There can also be relays for the engine that can get stuck in the ON position and can be checked with a voltage meter at the battery.
4. Are the battery cables and ground cables at the battery tight and clean
I dont think water inside the door has anything to do with it, as long as the window and door lock switch is still working. I would make sure the door is closing all the way and not leaving the interior light ON.
Now, if the engine turns over, but will not start you have a totally different issue going on and the battery/alternator are not involved in this issue. An ignition coil, fuel pump, sensor etc. would be the culprit in that kind of situation.
We got a new ignition coil put on our car recently, but the young mechanic, who I think was only in his early 20s at the most, refused to do a test drive on the car, right after it was installed. I found that strange, but about a few weeks later, the check engine came on.
Now, a year ago, this cop who was not helpful at all, insisted we keep our car window rolled down all the way to the base of the window when it was pouring rain out!
It is a car whose door & window units are powered by electricity and that power unit for the doors/windows is on the driver’s side door & rain was pouring that power unit for several minutes, while the cop, insisted on us keeping the windows rolled down, though we were the ones who called the police for help!
We’ve always had trouble even opening the car doors on the driver’s side door, and I know there was rust occuring inside the driver’s door, for a mechanic looked at and noticed rust inside about 6 months after that cop did that to us!
I’m wondering too, if we are getting our battery draining, because, there’s a short in the engine, due to the rain pouring over that electrical unit on the driver’s side door?
I’ve had at least 3 battery, brand new installed in our car, in the last few months, and I’m afraid every time we get into our car, it won’t even start, because it’s done that before, right after we got a brand new battery installed?
Anybody heard of a drain on an brand new battery as a result of a remote autostarter being installed? Have a 2005 Honda Accord. Installed a new battery 10 motnhs ago and only started having problems about a month after a remote starter installed and not having used vehicle for a week in cold weather.
ANY electrical device that is drawing power from the car battery can cause a drain on the battery. Your remote starter could be installed incorrectly and not properly grounded, or a switch or relay could be faulty causing the remote start feature to be in the ON position all the time. I see this a lot with aftermarket stereos and amplifiers that have been improperly installed into the main vehicle fuse box on a circuit that is always on. Your mechanic can check for a drain pretty easily, but tracking down the drain to a specific component can sometimes take lots of time. I would check for a drain at the battery, then disable your remote start kit to see if the drain goes away….if it does, you will need to go back to the installer and see what they can do. Most mechanics will not be familiar or interested in spending time trying to figure out how the thing SHOULD be installed.
I have had the some problem and my fault is with the alternator, Voltage regulator. It has been throwging out 20 amps to battery and cooking it so drains down very quickly. so will replace reg and get new battery. Hope this gives you something else to look at.
I have a 2000 Toyota 4Runner with similar problem. Battery dies after about 3 days. New battery, same problem. Took it to my mechanic who narrowed it down to the circuit that controls power windows, sunroof, etc, but could narrow any further than that (honest in that he said he could keep looking but it may take hours and he didnt want to charge me without asking if that was ok). This car ran PERFECTLY for 10 years…UNTIL I received the car from my folks (it was shipped across the country) Courier mentioned something to me about my “funny alarm”. It is Toyota factory. Mechanic says it’s not the alarm, but as i mentioned ZERO probs until it was shipped. Any ideas??
I would unplugg/remove the power to the circuit board and see if the drain goes away. If not, you might want to try another mechanic with a new set of eyeballs. Tracking these types of problems down takes time and the better the mechanic the less time it could take and less cost past on to you.
You also might be able to buy a used circuit board from a junk yard to cheaply test/guess at his diagnosis. I have seen electric seat motors stick in the on position and cause a drain. Stick your head under the seats and listen for a humming motor noise
I don’t think the shipping had anything to do with this
Not really sure if the shipping has anything to do with it.
Hi
I have a Freelander 2, and my battery is drained every morning. I replaced the battery, after it was recommended, and the very next morning the battery was drained again.
Is there anything I can look at, anything, I have checked the lights, the hood, the doors, the radio, but nothing seems to be on. Could it be something on the engine itself?
Make sure there is nothing plugged into the AC or cigarette lighter like a phone charger etc. Then check the glove box and vanity mirror lights to make sure they are off. Anything more than that you will need to see a mechanic and have an “electrical drain test” done to see what is draining the battery.
Should be a pretty big drain to drain down overnight. Could be a relay somewhere, an electric seat motor that is stuck and running (listen under the seats for an electrical noise) or even a drain coming from the alternator or some other electrical component under the hood. This would be best done by the dealer who knows these vehicle well, this could be a complicated diagnosis and I would not trust this vehicle with this repair to just any mechanic.
I have a 1964 Chevy 2 Nova with a 6 cylinder 194 engine.Pretty basic stuff, right. This is not a regular car that I drive all the time,but I do crank it up every couple of days to keep the juices flowing in it. A few months ago, the alternator light was on all the time. I replaced the original 32 amp alternator with a Napa premium 37 amp rebuilt alternator. I also replaced the original external voltage regulator with a Napa external voltage regulator. After I installed the alternator and voltage regulator,everything seemed to be working fine. The alternator light would come on when turning the ignition on and then turn off when the motor is turned on, like it’s supposed to. I hooked up a multimeter to the battery to check alternator load. Again, everything seemed to be fine. All the normal readings. So everything has been fine the last couple of months. The other day, I went to start the car, and the battery was almost dead. I recharged my battery and when I turned the ignition on,the alternator light did not come on. The car would start but the alternator idiot light was not working. I replaced the alternator lightbulb, still not working. I connected my multi meter to the battery to check alternator load. While car is off, volt reading was 12.35. Turning the car on, it only went up to about 12.73, not the 13.8 or 14.00 volts like it is supposed to. I replaced the old battery just for the hell of it. Again car would start but again the alternator light was not coming on and I was still getting low volt readings with a running engine. After letting the car sit for about four days I went out to start it up, and my new battery was completely dead. Something drained my new battery. There’s no fancy fuses and relays in this engine. I have no trunk light. I do have a glove compartment light, as far as I know turns off, when the door is closed. Dome lights are off when the doors are closed except that the drivers side door does not activate the dome light when it is opened like it’s supposed to. The radio is always left off. I do have an old antenna toggle switch that is connected to wiring under my dash that I mess around with every now and then but the antenna motor has been disconnected and long since been thrown away. So I don’t know whats been draining my battery lately and has my new alternator gone bad? Why isn’t my alternator light coming on when the ignition is in the on position? Could the alternator have something to do with draining the battery while the engine is off? I’m stumped!! I would really appreciate any suggestions. Thank you.
Yes I would be a little suspect of a faulty diode trio inside the alternator as the culprit. You might also want to check for q faulty chassis ground or just add an additional ground to the system. I have seen alternators have an internal drain. You probably should replace the voltage regulator as well because you don’t know which failed first regulator or alternator or did one cause the failure of the other?
1st take the bolb out of the trunk, hood, glove conperment
2nd day if still drain battery unplug the neg of your amp or remove the breaker also find the breaker for your radio
3rd day if still drain battery make shure that all your door light are of sometimes the switch for the door fucks up so make shour that the light works when door is open
4th day if still drain battery look for any cables that might be tuching metal (look for missing insulation on cable)
try this steps to eliminate potential problems hope this helps
i have the same problem with my 1992 eclipse. ill let it sit for about 8 hours and my battery will be dead. thought it wss the stater so i replaced it. but still having the same problem. although replacing the started did help a little bit. mabey u could try that
On my 2004 odyssey once in awhile the ac compressor relay sticks closed. I haven’t determined if the relay itself is a fault or the computer is closing it. I think the contacts are probably sticking closed after you shut the van off and draining the battery. When the car is off I can pull the ac fuse or relay out and you can hear the ac clutch click. I did swap the horn relay and the ac relay to see if its the relay. If the relay is at fault someday the horn will stay blowing afetr locking the doors with the remote.