don't think battery is dead - been on a charger the whole time.
charger or battery tender? big difference....if it was a charger you cooked that battery....
you need to do a check on it before doing anything else.
If it worked prior to disassembly, and sat 6 months, it's not likely a gremlin snuck in and changed something on it's own...do the simple stuff first.
I see you have just arrived here, please understand we diagnose this stuff everyday, and it isnt easy to diagnose things like this over the net....there are a lot of people here that have seen it all, so pleas, listen to the cumulative voices of experience on this bike.