Brand New Battery Dead Within Hours

[Mmh9611]

1981 Cb750k. I just bought this bike and after a few days the battery started to struggle to start the bike. I swapped out the battery with a new battery, but the bike made it about 4 hours total (30 min of ride time) and it went 100% dead. What could this be?

 

[brettp]

Your charging system likely isn't charging the battery. Charge your current battery to full, then start the bike. Check the voltage of the battery while revving the engine. It should increase as the engine RPMs increase, but the voltage should not exceed ~14.5V.