Zax63

So, my S-class has a new party trick, I was hoping someone on here has seen it before and point me in the right direction; I am out of warranty and don't feel like replacing every part involved below to attempt to guess what the &*^ is going on.
The Scenario:
Battery intermittently drains to zero. No rhyme or reason when. I may leave the car for a week and it starts right up, I may leave it overnight and it's dead as a doornail. I brought it to the dealer to figure out. They left it on a meter for a week and, lo and behold, it functioned perfectly. I brought it home that night and came out in the morning and it was kaput.

But the plot thickens... The night I brought it back from the dealer, I left something in the car. When I approached the car to retrieve it, the dashboard lights were on. I opened the door, the hazards flashed a few times. I retrieved my item, closed the door, and the dashboard lights went off. When I approached the car the next am, the dash was again lit up. Attempting to fire the motor, the battery did not have enough juice left in it to turn over the engine.

I mentioned this to the MB tech, and he said "maybe the keyless go button is shorting or something, and the car is draining the battery".

Rather than replacing the dashboard, the entire keyless go system, and who knows what else, I thought I would check with the MBworld crew to see if anyone had any ideas.

Thanks in advance!

czum09

Your dash lights light up when the car senses the key. Is it the original battery? What does your voltage look like while driving?

Zax63

Nope, it is a 2 year old battery. Haven't checked voltage when driving, but just drove 600 miles at night and no battery issues.

czum09

Turn key to on position, tap the R button three times, scroll to voltage, start car. Go for a drive with voltage displayed, report back with what it does!

Zax63

14.0-14.2 the whole time, the majority of the time it was 14.1.

corsaschnell

Check the battery cables for loose connections. Also, could it be that your alternator is intermittently not charging the battery enough thus causing the drain the next time you attempt to start it?

Zax63

nope, that has been checked. Dash randomly comes on in the middle of the night draining the battery. Probably in the keyless go system.