Battery size for my 525i?

[RJN42]

I recently bought a battery from my 2006 BMW 525i. Apparently it was smaller than the original battery that was in there. Since insulation, I’ve been dealing with a minor flutter of the RPM when idling at a standstill but not while driving. Could this be because the smaller battery is not putting out enough voltage? I’m just hoping it’s not the voltage regulator attached to the alternator. Also, I have something to do with the fact that the battery is only a few months old and it’s 42% when it’s fully charged. So obviously a fried battery. My OBD sensor and the BimmerCode reading indicates voltage regulator fluctuation and all source of other kind of voltage issues in regards to lack of power. What is the exact size or type of battery that I need from my Beamer that is affordable?

[DanG]

Why not just buy a BMW battery from the dealer? Usually they are not more expensive than an after market battery.

[ctcarbonari]

In its simpliest terms, the battery's job is to start the car. Once running, the alternator takes over.

All new batteries installed need to be registered (BimmerLink can do this). It let's the IBS know "hey, this is a new battery"

If a battery of a different size or capacity is installed then it needs to be coded (BimmerCode can do this). It let's the IBS know "hey, this is a different Ah rated battery so charge accordingly".

When you say your battery state of charge is 42% when fully charged is that after you put it on an external smart charger?

In any regard, I'd fully charge the battery thru the jump points. Code & register the "new" battery then go from there.

+1 to Genuine BMW batteries from the Dealership. They are competitively priced and meet the exact specs (whereas aftermarket batteries often have slightly different Ah ratings)

checkout www.realoem.com to figure out which battery size your Bimmer was originally spec'd for.