So I didn't drive my truck for about a week and a half and went to start it a couple days ago and the battery was completely drained to the point I couldn't even unlock the doors using the key fob. Tried to charge it and no luck, since it was less than a year old returned it to autozone and picked up a new battery. Installed new battery, truck fired right up and problem solved. Go to start the truck today and battery is completely drained. I didn't leave anything on, headlights off, dome lights off, no accessories plugged in that could possibly drain the battery. So Im perplexed what could possibly be draining the battery in just a few days? Truck is a 2010 Tundra with about 120000 miles on the clock.
September 07, 2025, 09:58 AM
ScreamingCockatoo
I've seen everything from a stuck relay to a bad alternator. My 1978 corvette has a courtesy lamp timer that will drain the battery. Even with the lamp and chime unplugged.
He who fights with monsters might take care lest he thereby become a monster.
September 07, 2025, 10:28 AM
1lowlife
I know it seems simple, but make sure your battery clamps are clean. I've had that issue on my 2005 and 2014 Tundras.
You'll need to check for a parasitic drain with a multimeter. A small draw is normal; ECU, clock, remote start/alarm, etc..
Also periodically check the water level of the battery. I got so used to sealed batteries that when I bought one with caps, I totally forgot to check the water levels.
I love my Tundra, got 11 years out of my 2005, before getting the 2014.
Good luck..
September 07, 2025, 10:48 AM
egregore
A sticking relay can be found by a thermal imager, a laser thermometer, or just plain old feeling for one that is warmer than the others.
"The Almighty, He put some livin' things on this earth so a man can eat." - Festus Haggen, Gunsmoke
September 07, 2025, 11:02 AM
Cookster
I was experiencing the same issue with my '04 or '05 VW Passat, and my local mechanic was not able to track the draw right away.
After picking up a friend to go somewhere they asked, "Why is the seat so warm?" after getting in the car.
Viola!
Even though the heated seat was not 'on', there was a short-circuit somewhere, maybe w/the dashboard switch, I do not recall exactly, but after the problem spot was isolated and fixed, no more draw / dead battery.
Something to check anyway.
Good luck!
__________ "I'd rather have a bottle in front of me than a frontal lobotomy."
The butcher with the sharpest knife has the warmest heart.
September 07, 2025, 01:21 PM
honestlou
Is the truck bone stock, or is there anything aftermarket installed? Lights, winch, stereo, dashcam, GPS, anything? Check all 12V accessory outlets and all USB outlets. Check trailer hitch plug. I have seen modules for aftermarket radios that worked properly, but developed an oversized draw by preventing the vehicle from going to sleep.
You can use a meter and pull fuses one by one to find the circuit with the draw, but you kind of need to know what you’re doing. Trip the door latch so the truck thinks the doors are closed, and wait for it to go to sleep. Then pull and replace fuses one by one- goes a lot faster if someone else is watching the meter. And of course just anything that causes a current drop isn’t the culprit- lots of circuits can have very small draws- but when you pull the big one you’ll know it.
Check your headlight switch. Possibly dome lights are on but dimmed enough that you didn’t notice.
September 07, 2025, 05:51 PM
architect
Car lead acid batteries appear to be designed to support a high load/short duration use (like starting the car). They do not seem as accommodating of low wattage long term applications (like charging cell phones). Sit an hour or so with your cell phone plugged in while the engine is not running, and don't be surprised that the battery lacks enough juice to start the car, learned this the hard way. Probably not new wisdom to many of those here, but it is wise to plan ahead. A portable jump pack is a lot cheaper than calling a tow service.
So finding the parasite is probably your best option, and you might have to buy a clamp-on amp meter to do so.
September 07, 2025, 07:20 PM
shovelhead
Some possible causes. Alternator, ECM/VCM/PCM, TCM, Body Control Module, radio memory/display, security system either factory or aftermarket ones. Faulty ignition switch, cooling or blower fan relay failure.
Parasitic load usually doesn’t kill a battery that quick, in dealerships we only usually pulled fuses on new vehicles on the lot if not run for over thirty days. Something is going on there.
-------------------------------------—————— ————————--Ignorance is a powerful tool if applied at the right time, even, usually, surpassing knowledge(E.J.Potter, A.K.A. The Michigan Madman)
September 07, 2025, 08:07 PM
mrvmax
One of the YT mechanic channels said those insurance company USB monitoring devices drain batteries.
September 07, 2025, 08:42 PM
blueye
About 3 yrs ago I decided to get a phone charger with a digital readout for my truck. Battery was about 3 months old. Let the truck sit for about a week of non use and went ahead to start it and run some errands. Dead battery, decided to unplug charger and never had a problem since.
September 08, 2025, 04:45 AM
calugo
quote:
Originally posted by honestlou: Is the truck bone stock, or is there anything aftermarket installed? Lights, winch, stereo, dashcam, GPS, anything? Check all 12V accessory outlets and all USB outlets. Check trailer hitch plug. I have seen modules for aftermarket radios that worked properly, but developed an oversized draw by preventing the vehicle from going to sleep.
You can use a meter and pull fuses one by one to find the circuit with the draw, but you kind of need to know what you’re doing. Trip the door latch so the truck thinks the doors are closed, and wait for it to go to sleep. Then pull and replace fuses one by one- goes a lot faster if someone else is watching the meter. And of course just anything that causes a current drop isn’t the culprit- lots of circuits can have very small draws- but when you pull the big one you’ll know it.
Check your headlight switch. Possibly dome lights are on but dimmed enough that you didn’t notice.
Bone stock no aftermarket accessories whatsoever and verified all the lights are off inside/outside the truck.
September 08, 2025, 04:47 AM
calugo
quote:
Originally posted by shovelhead: Some possible causes. Alternator, ECM/VCM/PCM, TCM, Body Control Module, radio memory/display, security system either factory or aftermarket ones. Faulty ignition switch, cooling or blower fan relay failure.
Parasitic load usually doesn’t kill a battery that quick, in dealerships we only usually pulled fuses on new vehicles on the lot if not run for over thirty days. Something is going on there.
One odd thing that happened when I hooked up the battery charger is the blower fan came on as the battery charged but the ignition was off so maybe a clue to my problem.
September 08, 2025, 07:53 AM
octo
high blower relay is stuck;common in the seventys.
September 08, 2025, 08:21 AM
robbiedog
Slightly ot, but my 2018 GMC Yukon's battery died and could not be charged up. Looked on youtube on how to change the battery.....it's almost rocket science compared to the "old days". I decided to forgo the 2 hour plus time it would take to change it, including the possible damage to my back trying to wrestle the damned thing out of a very tight space, and have it towed to the dealership and have them do it. Total spent was $538, including the tow, all to change a damned battery.
September 08, 2025, 08:21 AM
1lowlife
quote:
Originally posted by calugo: Bone stock no aftermarket accessories whatsoever and verified all the lights are off inside/outside the truck.
I was going to email you this info, but you don't have an email in your profile.
You can find your wiring diagrams on Tundras.com Complete with a power source diagram for all circuits. That way you can see what runs off the BAT, IGN, etc. It also has all your ground points. It might help in tracking down your draw. Although you'll need to create an account and log in to view it.
If you'd like me to send power source diagrams to you, please send me an email, and I'll be happy to do so.
My email is in my profile.
September 09, 2025, 02:59 PM
neverfollow
Not sure if you figured it out but my 2019 BMW X1 battery died 1 year after install. BMW replaced the battery under warranty and 3 months later the unit died again. During diagnosis they discovered the small battery that powers the emergency contact system (think post accident) was faulty and kept drawing current - draining the battery. Fairly quick fix and no more main battery issues.
September 09, 2025, 04:16 PM
cyanide357
Do you have anything plugged into the ODB port?
September 09, 2025, 04:42 PM
shovelhead
If you have a blower control module that is “loose” and I mean as not attached to or as part of another component I’d replace that.
But, in todays world of electronic controls, like in our Jeep Liberty the blower relay could be integrated into what they call a blower control module which takes the place of the blower relays and the blower motor resistor which controls blower fan speed. Ours failed, the blower would stay running with the key off.
They are commonly accessed from in the passenger compartment, located where the fan will blow air across it to dissipate heat created especially when on lower speeds as those are done through resistance. Back in the bad old days blower speeds were done through coils of resistance wire.
-------------------------------------—————— ————————--Ignorance is a powerful tool if applied at the right time, even, usually, surpassing knowledge(E.J.Potter, A.K.A. The Michigan Madman)
