Mr.Cheezle

Hey folks,
Need a little guidance.
Several weeks ago our r500 ran into some electrical issues. While driving I lost control of the wipers, rear drivers side window, and I believe the radio.
I tried to shut the engine down, but when I removed the key, the engine was still running! Eventually the engine stalled or shut itself off and wouldn't restart. I towed it to a local shop, where the young fella diagnosed a dead auxiliary battery. He had tested the main battery and the alternator - both of which he said passed his tests.
Fast forward several days - of which I had been driving the vehicle, incident free. (Wipers/Windows/etc all worked. It started and stopped without issues) But today, after driving it for about 30 minutes, I stopped to duck into a store and when I returned, the car wouldn't start. It would crank, but not turn over. It fired up with a boost. I let it run for another 30 minutes then shut it down. Wouldn't start again - but would with a boost.
Is my main battery causing fits? Maybe the SAM? I'm at work and can't check the voltage on the main. I was going to put the trickle charger on it when I got home - assuming I will make it. I'm unsure of the age of the battery, but it has to be at least a few years old.

chassis

A few years old with the problems you describe = time for a new battery in my opinion.

Mr.Cheezle

Car was left at work for a period of 8 hours. When I tried to start it - it fired right up without a boost. Drove home. Parked it in the driveway, tried to fire it up after about 20 minutes and it wouldn't start. Tested the resting battery and the voltmeter reads 12.3 volts.
Might the battery be old enough that I'm not getting enough cranking power? Would the warmth of the engine have anything to do with it?

Edit: Definitely starts once it cools down. After some reading seems like it might be the CPS?

kombifan

If origibal batteru is original replave that.

Check front and rear sam for water and dampness. That will explain uoir whole electrical mess too

chassis

Voltage read with a voltmeter does not indicate battery condition. It needs to be load tested. In my opinion if there is any question about battery condition, and in this case there appears to be question, it's time to replace the battery. It's the cheapest, or one of the cheapest, parts in the chain of things that could be causing the symptoms.

Mr.Cheezle

Thanks for the feedback folks.
What size battery am I looking for?
I know I need an AGM.

chassis

Confirm this:

Mercedes part no. 000-982-00-08

Group 49 AGM 92AH 950CCA

I like Varta but I'm not sure they are sold aftermarket in the US. I bought a Varta from a VW dealer for my previous vehicle.

Call your local dealer for a price, it might be similar to a local auto parts store.

Mr.Cheezle

Thanks for the info.
I'm now getting the red battery warning light - so I'll take the car to get the battery load tested, but I would assume at this point that the battery has to be the main culprit.
I'm in Canada, so sourcing these batteries isn't the easiest. Not a lot of options

chassis

I have purchased batteries from car dealers in the past, the prices were comparable to retail auto parts store. Have you called your local MB dealer? A battery is a normal replacement part and part of the cost of operating a vehicle.

Mr.Cheezle

Update:
Finally got my hands on a battery and put it in yesterday. So far so good. Had it out for a rip last evening and everything seems to be in good working order

chassis

Great news. What brand battery, and where did you source it?