Have you ever had a battery go after 5 months?

So i was playing in the mountains today, we stopped for lunch, and when we were ready to set off again my bike wouldnt start. when i turned the key the lights came on as normal but only for a second, then nothing would happen after that, and i mean nothing. after various trouble shooting ideas. we took the battery out and off to a auto parts store. do you know how hard it is to find a suto parts store in the mountains thats open on a sunday? i do now. they tested the battery and said it looks like it has a bad cell. im thinking good, just a batttery not a major electrical problem. get a new battery and everything works fine again. but now im wondering if something screwed up the battery. i should also mention that the connection for the main fuse relay was corroded and one lead looked burnt. which it didnt have that the last time i checked about a month ago. i know about the r/r problems but this has a aftermarket one, not sure of the type off hand.

any thoughts? just bad battery? need another r/r? maybe a stator? i know i should start checking things with a volt meter, but i dont have time for that in the next few days.