Amp Eating Automobile


Does anyone have cure for a 2005 Lexus E350 that discharges the battery when it is parked for several days. Test voltage shows a decline from 12.71 to 11.70 in 6 days of sitting in the garage. Two weeks at the airport requires a jump to start.


Something sure and simple? Yes. Get a battery disconnect from Walmart.
Or, go the red banner, above, and type in something about battery discharge in the keyword block.


do a parasitic load test and find out whats pulling so many amps.20 min job


There is a drain on the battery. It could be something as simple as the glove box light staying on or the light in the trunk. You can check these lights yourself. If you can’t find something staying on then someone with expertise in this area will need to look at it.

As suggested a battery disconnect switch could be a option but I would advise against it. This car has too many modules and computors in it and they don’t like being disconnected from battery power. They will perform duties while the car is sitting and will take up to 1 hour to power up after they have been disconnected from power. Switching power off and on could also damage them.


You do need to check for a current drain. If you aren’t able to do this yourself then take it to a good shop and have them do the work. This is a pretty simple problem and any good shop should be able to find the trouble fairly quickly.


Might be a good insurance plan to buy one of those booster packs and keep it in your trunk.

BTW - switching power on and off is not going to dammage your vehicle electronics. But I agree that the battery disconnect switch is not the best solution.


There are 3 possibilities as far as I can see. First, there is some light or other accessory that is staying on when it should not. Second is the battery is self-discharging. Third is a bad alternator. I list them in order of most to least likely. It’s pretty easy for a relay or switch to get stuck and keep a light on when it shouldn’t. Connect and ammeter to the negative side of the battery and then start pulling fuses to see when/where the current drops a lot. Whichever fuse you pulled at that point is the circuit you need to check out. If that doesn’t give you a culprit, then try disconnecting the battery negative post for a week, see if the problem still occurs. It it does, then the battery is bad. Finally, if none of the above works, have a good shop check the alternator. Discharge through the alternator requires 2 diodes to both fail shorted, and to be adjacent in the circuit. It’s unlikely, and usually would discharge your battery overnight.


I will add one more. The battery may not be able to hold a charge.

So look for the parasitic drain and have the battery tested. You also could disconnect the battery and see what happens after a few days. Remember that disconnecting the battery in a modern car can have some unexpected results.


There you go again… spouting off about things you know nothing about. Damage can and does occur to automotive electronics when you continue to disconnect and reconnect power to them.

I’m not going to get into a pissing contest with you about it though. I have the experience and the background in automotive eletronics. What’s your background again in the AUTOMOTIVE field??? OH… that’s right… NONE!!


You’re right - electronics have different physical properties when they are in an automobile copmpared to anywhere else.