i have a cbr400rr nc23 which ive had for approx a year which i love and i think is great

but just recently (as it has started to get cold) it developed a little missfire randomly every now and again, i ordered up a set of plugs thinking one was breaking down.
however before they arrived ive noticed the missfire gets a lot worse with other electrical items running (horn, indicators lights etc)
i then started to think it may be battery charging problem, so got my meters out and the bike is pulling 14.2ish volts on idle with basic engine running and about 13.8 with lights and indicators. ive also drop tested the battery and it passed fine some where around 14.8amps
however last night when i parked it up it died before i had chance to swtch it off and when i tryed to restart it, it growned like it had a flat batt, and didnt turn over, so after telling the mrs all about it i went to grab the battery charger out, but before i conneted it up i thought id give her one last chance to start on her own, and she cranked fast and started well

i was wondering if anyone had had the same problem
im wondering if it could be a dud battery or if its over charging and cooking its self or maybe the reg rectifier?
HELP PLEASE

thanks jackson