Buy a cheap volt meter. Buy a battery charger that is rated at 1.5a and not under that number you shop for a charger. That's like you tagged teamed walmart and found both. Are you back home with those two items?
1. Charge the battery before attempting to drain more out of it.
2. Say you charged the battery and now you have the volt meter set at the 20v scale.
3. Start the bike, let it idle, what does the volt meter read? 14+v is a good sign at idle.
4. That says the stator is putting out the correct amps, the volt/reg is regulating a well charged battery, your CB did not pop.
5. The CB has not popped. The battery voltage has stayed the same or is dropping very slowly holding the volt meter there with the brake light on you go stepping to that step.
6. There is this term called 'total loss.' The battery will run the bike until there is a breakaway limit to the volts needed and that CB broke the chain from stator to v/reg to CB to battery+ side.
7. If the CB pops, a recall was mentioned, NAPA the crap pa out of it and match a US made part, unless they hand you the same breaker brand, then run a 40a fuse as posted or buy a harley 30a CB and use that.
8. If again you check voltage and that fuse is hot or ticking, you have a direct short is why it's popping now or just make sure when you start the bike you feel that fuse and keep using it.
9. Probably nothing wrong with the fuse... IF...
10... She no pop on start up.