Not sure anyone has run into this but I bought the Sony 850 with battery and ordered a extra one with same exact model number. But the spare sometimes works but mostly get a warning and won't work. This is making me a little mad since it is a Sony battery and not some off brand unit. I had the same issue with a A55 battery too although that was off brand.
More concerned about the 850 I have to have two batteries. Any idea's on this. Like to order another but afraid i will run into the same issue.