That being said, I think yours should work ok. Mine has h27 firmware, & it seems to work on any of the 4200mah packs I have. Only thing that might be an issue, is if you have to do alot of repeaks, I've noticed if you repeak a pack too soon after it originally peaked, then the charger might not stop, & end up overcharging the pack(had it happen once to a pack of GP3300's, thought I should repeak it but it was too soon & I pretty much cooked the pack as a result). And while yours may say c27, it sounds like your charge modes are the same as mine, so I'd think its peak detection should be the same too(the newer versions add a P0 charge mode, but the regular P mode ours have seems to work just fine....