GT-i9100 user here. (No bloody AT&T or Vodaphone versions, Exynos not OMAP).
Got myself a GC110. Pleasantly surprised to find the original battery for my old Galaxy S2 *fits the camera*. Well, not completely perfectly - I can stuff it in and it barely fits, and I'll need a bit of work to get it out, but the camera works, no power or voltage problems. I had it running up to 20% left too.
I first suspected as much when I realized the only thing different on the new batteries were the serial numbers. But... the snug fit I got here precludes the "taller" official extended from fitting, let along things like the huge Momax one.
Got an extra GC110 battery and charger as a bundle, the Galaxy S2's battery works on the charger. The GC110 extra battery does indeed work on the S2, and by extension the GC110's original battery. So now I have 3 batteries and 2 devices. Joy.
Move "sig". For great justice.
Galaxy S2 i9100 OmniRom Nightly 0106 / Dorimanx 10.43v60 beta
Galaxy Camera EK-110 (stock rooted) (It only ever came with 4.1.2 so.)
Ouya (stock rooted) (it only ever came with 4.1.2 so.)
Liquid Community ROM 1.4 (Acer Liquid)
O2 XDA Atom WM6.1 Kuruma Final
HTC Touch Elf Opal Ultimate 3.2.1
LG KS20 Kiss20.4