High-G FJR Junkie!
Join Date: Jan 2013
Location: Millgrove, ON, CA
Letting a battery sit for a month or more isn't good without a battery tender hooked up.. the bike has a parasitic draw to keep clocks, etc. powered up. Once a battery gets down to 12.5 volts, it is at 50% charge, lots don't realize that. FJR's like a fresh battery, so take care of it.
Running for 20 minutes is not going to properly recharge a low battery. Slow longer charge is better.
Stator checks as recommended by John will prove stator is OK, they don't fail on these bikes... common issues are poor connections to the regulator, check those connectors. Gen 1 did not have as good a regulator as later FJR's, but rarely do they fail. For an upgrade, find a used genuine Shindengen FH020 off a later Yamaha... FJR, FJ-09, etc. I believe the connectors are the same on Gen1, but check (there are connectors available... Roadster Cycle).
Keep yer stick on the ice....
2014 FJR1300A - Root Beer (sold)
2009 CBF1000A - Sienna Red
1999 VFR800Fi - Pearl Shining Yellow