Lexus dead battery

On long trips my wife pulls off to nap for 20-30 minutes. Three times recently the battery was dead on the 2002 Lexus ES 300. There is no problem when she turns off the car and leaves it at night. Is this related to remaining in the driver’s seat when the engine is off, or do we have a short somewhere? If so, where do we look?

It’s not because there is someone in the car, unless she is using some electrical accessory while she’s napping. There is no good reason for a battery to be dead in 20-30 minutes if everything is off. Is everything off while she’s napping?

If the battery is original I think you should have it tested. It may be time for a new battery, but I still can’t explain why the battery would go dead in a half hour.

What happens when she tries to start the car after a nap?

This is interesting, but I think that you may need to ask your wife to demonstrate what she does while you watch carefully.

Some cars leave the radio playing after you turn off the car, until a door opens and closes. Running the radio should not run down a battery in 30 minutes, but I wonder what else stays on? The solution might be as simple as opening and closing the door before falling asleep.

If this is the original battery and it has recently been run completely down three times, there is no need to check it, it is ruined. Maintenance free batteries do not like to be deep-cycled, and a six year old battery won’t tolerate it at all.

I hope your wife pulls over in a very safe place. Wasn’t it Michael Jordon’s dad who met his end while napping in a Lexus?

Like Manolito said, I think something’s on when the key’s turned off but the door’s not opened. I don’t think it’s a short.

I think that your wife is napping with the radio/sound system ON. When the engine is turned off, and the ignition key is, later, placed in RUN position, the interior fan will run, even though the A/C isn’t cooling, nor, the heater still putting out heat (except residual).
It probably happens this way: She stops the car, removes the ignition key, goes to refresh, comes back, turns the ignition key to RUN (to power the radio, and naps.
You could teach her the power of the ignition switch ACC position.

There is a pretty good chance that the problem is related to heat, since the car does start after sitting overnight. If you have not replaced the battery I would do so with the best replacement you can find (even with this it’s under a $100).

I would even replace it if the tech says it checks out ok, since some failure modes just don’t show up using test equipment.

If things fail after replacement, then you’ll at least know it is not the battery.

When replacing, have the tech carefully examine the heavy positive and negative feed wires for bad crimps, loose bolts, or other problems.

That’s got my bet. (Somewhat based on what I’ve seen my wife do.)

Even with the blower and radio on the battery should still start the car after 30 minutes. Assume a 75 Ah battery. The blower motor is 20 amps tops. The radio takes, what, 5 A? That is only 13 Ah at the outside

I have had the same battery problems with my previous 1997 SC 400 and in my current 1999 SC 400. The problem is most likely not with your battery or the alternator.

I have found by replacing the factory cable connectors to the battery with Marine type LEAD connectors that are painted, except for the areas in contact with the battery post and cables will correct the problem!

I discovered after numerous dead battery situations in both cars that the alternator was putting out the required 14.2 V (the nominal value), but the battery was not charging. Therefore the only problem could be that the charge was not getting to the battery. I replaced the connectors with new factory connectors that were flimsy aluminum. This did not solve the problem.

I finally got a good conduction current into the battery after replacing the battery connectors with plain old lead type connectors that can be purchased at any pep boys for less than five bucks.

I have since utilized the Marine connectors in my 1999 SC 400, because they are painted on any surface other than connection to the cables and the battery terminal to prevent shorts.

Hopefully this will help correct your problem as well.

PS: my brother who is a certified mechanic actually uses spray paint or grease on the battery post after tightening the connection in order to prevent oxidation of the connection.