There are several possibilities:
The bike's battery is bad. This is by far the least likely cause, as the previous battery behaved exactly the same way. The chances of having two batteries fail sequentially in the same manner is very low.
The battery is not being charged when the motor's running. If there's something awry with the charging circuit or its ...
This answer assumes there's a fault in the electrical system somewhere.
With the bike off, remove the cable from one terminal of your battery and put a multimeter (IN CURRENT MODE!) in series with the battery terminal and cable.
You should see zero amps flowing through the meter. If there is current flow, even in the milliamps range, you've got some kind ...
Very low tech solution - I had a bicycle mirror with a loose ball and socket joint. Pulled the ball out, put it in a plastic-wrap baggie, and pushed it back in. Trimmed off excess baggie... Mirror is as tight as brand new.