Just joined this medium to see if I can get some help. I have had a few battery replacements between November 2015 and January 2016 with a few dead battery issues between January and as recent as today (hence my search for answers!). I am stumped and now thinking of getting rid of my Lexus and permanently saying goodbye to ever owning another one! The battery company tells me the last battery was fine but replaced it anyway when they saw how frustrated I was. Now my car will leave me in parking lots and totally will not start if I don't drive it for a few days especially in the winter time. The car is always in a garage at my home. I do see a few problems online and saw something about a third brake bulb on another site. However, was not able to see all the details so it can help me. I am NOT mechanically inclined at all so things too complicated will go right over my head! My alternator is fine and NO, there are no lights left on or door ajar! HELP!!!

 

Welcome to CL.

OK..... if the battery keeps draining every couple of days, and it's not a light-bulb that you can physically see, then the first thing you usually want to check is if a hidden light bulb, one it is not normally seen, is staying on even it should be off. Examples of this are underhood lights, trunk/cargo-area lights, glove-box lights, and (if applicable) lights inside of closed cubby-compartments. Some of those can be difficult to check, because if you open the lids enough to see the bulb on, the switch to trigger it will have already released, and it would be on anyway. Try to shut the lids very slowly, as you keep an eye through the small slit as the lid shuts, to see if the light inside goes off or not. In some cases, a technician may have to check it with a current-draw meter, or something to detect a short. If the bulb stays on even as the lid closes completely shut (provided you can see it), then either the on/off switch for the bulb is bad (needing replacement), or you have a short somewhere. In the meantime, of course, you can always pull or unscrew the bulb out of its socket, and simply not use it until the system gets repaired.

And, yes, as you note, it will be worse in the winter months, because batteries need more power (measured in cold-cranking-amps) to start a cold, stiff engine, and the power-drain of the stuck-on-bulbs will make the battery even weaker. What might be marginal starting capability in warm weather could, at freezing temperatures, mean a call to AAA, jump-starting (which can be risky to the electrical system in modern cars), or getting out the battery-charger.

 

It is not that difficult to trouble shoot parasitic drain. But you need to be a little bit mechanical inclined and need a ammeter.
1. connect ammeter in series with the battery
2. Close all doors, turn off all lights, remove car keys (if available).
3 Begin removing each fuse one by one until you will find the one that creates parasitic draw. This will let you isolate the problem.
It could be time consuming depending on the issue.

What is year/make/model of your car? Some issues have been previously diagnosed on specific model forums. Search model/year specific forum.
For example I owe Acura TL 2008. When I had issue with parasitic draw I found my cause withing minutes by searching acura tl G3 forum which is a well known issue to g3 community.
good luck

 

You're going to need some basic tools as listed above to find this issue. Or, see a technician.

Common causes for this are computers/modules that don't go to sleep, bad door switches, bad relays (sticking on) or aftermarket add ons like alarms/remote starts/amplifiers not shutting off.

If you have an aftermarket ANYTHING electronic installed, pull the fuse/unplug that and try again. If your problem goes away, lose that accessory.

Otherwise, get that ammeter or a good electronics technician.

As for Mike's suggestion above about checking cubby lights, an easy way to do this is to set the video recorder on your phone, pop it inside the cubby and close the door. Check the vid and verify the light went out.

Good luck! These can be annoying. And it's by no means any reason to stop buying Lexus! I work on all makes, and Toyotas do this the least out of the other brands. Chevy is particularly bad with poor quality modules doing this to batteries.