Hi All,

I'm working on a friends new to him 2008 GS350. The battery is dying for no apparent reason. The alternator is charging at around 13.8 volts. We cleaned the terminals. The battery is 5 years old, but it load tests just fine with an old school resistive load tester. One clue is that we were hanging out near the car having a few drinks at the campfire hours after the car was sitting unused and twice that we noticed the car reacted flashing the lights as if the lock button was pressed on the remote. The key was in his pocket, but there is little chance the buttons were pressed, certainly not twice. I'm wondering if it couple be a defective key that is talking to the car for no reason? Before he left we tested the voltage and it was way down under 11. The car did start and get him home fine, but clearly there is an issue.

I'll run the draw tests fuse by fuse the next time he's over, but I'm wondering if there are any usual suspects on this particular car.

Thanks!

 

Since the alternator is not charging adequately, I would start there. Read up on alternator function and voltages; what you report is not healthy.

 

The alternator seems fine, charges the battery no problem. The problem is when it is sitting unattended. Unless there is a bad diode in the alternator causing the draw. I'll recheck everything, but there seems to be a serious draw pulling the battery way down in less than 1 day. I still need to run current draw tests the next time he stops by, I was just wondering if there was a common offender on this model.

Thanks!

 

5 years is getting up there for a modern- day battery. It could pass the load test, but is unable to maintain good charge over time. Have you done a draw test at the battery terminal?

 

I agree 5 years is old for a battery, but I want to make sure there is no draw first. I don't want to damage a new battery by deep cycling it. I haven't done the draw test yet, again it's not my car so any further testing needs to wait until he brings it back over. As long as he frequently drives it it's fine.

 

Why do you believe 13.8 is not adequate? Although I do believe that checking alternator amperage output is the better test.

 

The value should be 14.4 or a bit higher. 13.8 is barely adequate to overcome resistance to charge a battery of 13.2V nominal voltage. The alternator is about dead if that is peak charging voltage.