dol4er

My battery is 6 years old. I used the service menu on the dashboard to access the vehicle data and the battery stats. The key was on position 1 when I checked the voltage and it was 12.1V, then 12.0V.

Does this mean that the battery is ok? What voltage means that the battery is in poor condition and must be replaced?

white46

Staying around 12v is good without being charged. Once the car runs, and alternator kicks in, voltage should be around 13.5v.
I had my original battery just replaced about a month ago. For 9 years, 120,000km, it was great.

mrbrannin1

static battery voltage for a fully charged battery is 12.5 volts with the engine off.....
if you load test the battery and voltage drops below 9.6 change it... no if and's or butts about it.... even if its showing fully charged before you load tested it.....
and while the car is running battery voltage should be 13.5 to 14.5 range..... at the battery or alternator.......
take into consideration with cold temperatures it will drop a few but thats when the CCA's (cold cranking amps jump in play)
hope this helps!!

edgalang

I'm in the same boat, except I use my hardwired radar detector for constant voltage readout and a battery tester to measure CCA.

Current CCA (5.5 year old battery) is 580 (stock is 800). Battery testers generally will fail a battery at around 20% loss. I plan to replace mine at 70% when it reaches 560, so hopefully around the same time the car reaches 100k miles (currently 90k).

dol4er

Is checking the voltage during and right after starting the car a good load test?

mrbrannin1

yes check it while running in the range of 13.5 to 14.5 volts..... after turn engine off and remove surface discharge b/c the battery is techinally fully charged b/c you were idling it....
so with that being said turn the headlights on and dome lights and radio for like 5 min.... turn everything off then test the battery again...

dol4er

After I started the car, it dropped to 10.6V... is this ok?

Demvang

No, it should be in the range of 13.5 - 14.5 as Mrbrannin1 mentioned. I think that 6 year old battery is on its way out because it's not holding charge.

dol4er

I meant 10.6 immediately after the start of the engine. It goes to 13.5 - 14.5 immediately after that when the alternator kicks in.

mrbrannin1

thats fine for like a second or 2 thats what the term voltage drop is... as soon as you cranked the car if it dropped to 10.6v for a second and immedieately goes up to charging range to 13.5-14.5volts then ure good..... as long as it dosent drop below 9.6 on a load or start up...

dol4er

Thank you. I will measure it from time to time and see how it goes.

mrbrannin1

holger

Question for the forum: will the local dealer replace a battery under warranty if it fails the test? I am coming up on the 4 year mark this month, so warranty is about to expire, and my battery is getting tired (used on many short trips). Cold mornings have a more sluggish start. I used one of the newer conductance testers that measure the internal resistance of the battery and estimate its capacity. My oem 800A EN AGM battery reads at less than 60% state of health (about 470 cranking amps) warm and after a full charge. Do you think the dealer will replace under warranty if their test confirms it is that low?

dol4er

Probably no, but it is worth trying

edgalang

I've always been under the assumption that car batteries fall under general wear and tear, and that the only warranty that'll apply to it is the battery manufacturer warranty (of whatever that years may be).

BUT...

With that said, thanks for confirming that it'll still start with 60%. I've been on the fence regarding my battery sitting at 73% (580). Now I can rest knowing I can push it to the next oil change (100k miles) before replacing it.

scrappykoko63

Battery light came on yest command shut off volt was 11.7.. after restarting car command came back and volt was 14.0 up until i did a few pulls went down to 12.0-12.2 nothing shut off car ran great. Can this be battery or alternator going?

loveisextinct

(New member here...greetings from Texas!) I recently purchased a pre-owned C250 (2012). Having the exact same issues with my car. 👆 Scrappykoko63 Were you able to find out what the issue was? Battery or alternator? Thanks in advance.