Bought my R56 last Summer. I've been fighting CEL and codes....AND
"Limp Mode". Took a look at my battery, and it's old.
I've seen a post on here connecting CEL's and other issues with
old batteries. Either low voltage, or possibly a short that will
affect the car.

 

All sorts of weird things begin to happen with the electronics when the battery starts to die. Take it in to any big box auto parts store and they'll check it out for you and replace it for you if needed.

 

You said it's old? I'd replace it, fly'n brick is correct, weird things happen with a marginal battery..

 

Keeping a "bad" battery in a car is a false sense of economy...
Sure you can get odd errors and issues...
You can get stuck...
But you can also shorten the life of your alternator...it will need to run at 100% every time you start your car for a longer time...and this also lowers your mpg...
So just spend your $100-160 and replace it if it is time!!
Get it tested.....I have seen "new looking" batteries be junk, and "dirt old ones" be perfect...