Hi ruprecht,
Just a fair warning, software issues are to be handled by Apple tech support who specializes in software and can also isolate issues to hardware related, in which case they can set up an appt for the customer then. Hardware issues, determined by those techs or via a customer insisting they want to set an appt up for a repair or replacement, are what the store techs handle. **Please note: If the store tech determines your issue is software related, you will be advised to contact software techs via Apple support, using the contact method of your choice.
Basically, If you show up with a software issue, you will most likely be redirected back to Apple tech support. Okay, 99.9% chance they will explain they are unable to provide appropriate software support, as they were not trained specific to that division. I'd not waste the trip.
One specializes in software. The other, in hardware.
Regarding batteries, Apple Support sw techs are ordering these for customers, which I feel sure someone pointed out and yep, the stores are overwhelmed by battery replacements alone. A walk in was never advisable but now, it should be emphasized it's best to simply not attempt one for ANY hardware issue. The store will reach out to give status then when battery comes in.