Process & discussion on battery types here:
Ampera 12V Battery Replacement Process

 

Make sure that it is suitable for use in the passenger compartment of a vehicle. GM specified an AGM-type battery for the Ampera. When I replaced mine I bought a Bosch S5 Battery (S5 Battery 027 5 Year Guarantee) available from Tayna or Eurocarparts (Eurocarparts will offer regular sales, usually at the weekend, or available via eBay for the same sale price).

 

Had this happen to me :

Parked the car on a slight upslope put the gear on P, released the foot brake (and that's when the car moved back by an inch or so)
Next day when I wanted to move the car, the gear shift from P to R was very hard to move and needed a lot more strength to do it once I managed to shift it to R a very weird thump was heard and the car went to .. .. wait to shift mode .....

Google it up 12v showed up as the culprit ..
In the meantime disconnected the12v negative wire and after 10 min the issue resolved it self...
My feeling was that the above issue was because of the car sliding back and having to force the gear from P to R as the 12v battery is relatively new... from that day I stop the car keep my foot on the brake then use the "hand brake " twice the release the foot brake and power down the car.

Issued never appeared again after that

Kind regards

Andreas