the 420 wouldnt start yesterday, and I jumped it with my Jeep. Im surprised my jeep battery could start it. anyway, It would run fine, which seems to tell me that the alternator is working fine. However, when i shut the car off, it wouldnt start back up or anything. Fine. Took the battery out to the autoparts store, and they said they tried two diffrent chargers, and the battery would not take any sort of charge whatsoever, either on the large charger or the small charger. I think the battery just went bad. It is a autocraft battery, probably from advance auto parts, but it is relatively new, only ~2 yrs old i would guess. So aside from replacing the battery, is there anything on the car that would cause the battery to fail like that?

and what kind of replacement should i buy, if that is what i need to do?

if your battery won't take a charge you need a new one. If you are asking if something could have caused it to go bad, yes, if the voltage regulator is bad (mine went bad at about 90k) it can overcharge the battery which can make battery unable to accept a charge. Battery can also go bad if you let it dry up, once that happens, it is too late to add water.

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2005 Mercedes C230k sport sedan, 6 speed
1987 Porsche 924S - 968-engined track car

ok. got a new battery. so can i put a multimeter on the battery leads and see what kind of voltage is there at the leads when the car is running? or what else do i test?
also- there is a wierd startup surge-lag-surge-normal rpms and then its fine. no problems when driving.

thanks.
mark

Some batteries are better than others. Some due to a manufacturing defect may lose a cell or two earlier than expected...I generally get about three years on my daily driver battery versus five to six on the light duty vehicles.

If your alternator is doing its job, you should see between 13.5-14.4 V at the battery terminals with the engine running (and accessories off). 12V nominal with the engine off. Anything beyond those parameters indicates a problem.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car