Replaced battery...now reading 12.1 volts....

[sudolg]

Battery died. (who knew that the cig lighter in the back didn't turn off with the car) Picked up a new Bosch from pep boys. Nice fit. I trickle charged the batt until my charger said it was fully charged. Installed it. I checked the voltage on the positive terminal and a ground and it showed 12.1 volts. Same when I checked under the hood using the jump start positive terminal and a nut on the strut tower. Car starts and drives like normal. Am I crazy? 12.1 volts? Before I pull the battery out and return it, just want to make sure BMW doesn't somehow step down the voltage so they could again be different than every other car on the planet.
Thanks!

Greg

[Weasel]

Nope, fully charged battery with no loads on it should be 12.65. But it is almost impossible to retain that voltage with the battery installed at the X5 will draw about 30-35 miliamps constant to retain computor memory all the time when off, and takes about 12-16 minutes to get that low as the car shuts off in stages electronically.

What I would check is the reserve capacity (RC) and amp hour (AH) ratings of the new bosch battery as those numbers have to match the OEM battery and are actually more important than the CCA rating! The alternators output is controlled by the DME to keep up with the vehicles high electrical load, and if the RC and AH ratings are too low the electrical load while running (headlights + heater + seat heaters, etc.) may be higher than the charge rate the battery can accept.

Here's a page with the basics on battery ratings.

[sudolg]

Yeah, the new batt betters eveything from the original (RC, AH, CA, CCA) It has been a consistent 12.1 every time I check so I think something is a little funky with it. I'm going to remove it and do some more analysing. I think I got a bad batt. Just wanted to check before I go through the hassel of removing it.

Thanks for the info.

[Weasel]

How long are you letting the truck sit before checking the voltage, and after how long a drive?

[sudolg]

So....here is what I did.... I charged the battery. I then installed the battery in the truck. I took it for a quick ride and checked the voltage. It is now indicating 12.1 volts every time I check it. The drives have been short since then.. let than 10 miles. But I did fully charge it before so I would think this would not matter.

[Weasel]

It may just be from the electrical load in the truck then. I regularly have cars come in that measure from 11.9 to 12.3 volts, and have no voltage issues... If you're worried about the battery's ability to hold proper charge, after charging or driving for a while remove the ground terminal to remove the electrical draw of the vehicle, then test across the terminals after letting it sit a few minutes to stabilize. It should have 12.65 at 100% charge, 12.45 would be 75% charge, 12.24 would be 50% charge and so on.

[sudolg]

OK. I let the truck go to sleep and then checked it. I had to leave the hood open or else I couldn't really check in sleep mode. So the result was about 12.4 volts now. I can't believe it was that much of a difference. Wow do these puppies drain when not running. My next step was going to be to remove the ground which I may still do over the weekend just to be sure.

Thanks a bunch for your help.

[Weasel]

Not a problem Sounds like you don't have any problems, so it should be fine!