2-3 days is not too long between charges for a good battery. Sounds like 2 problems at once. An old battery and a weak charging system. It will sit and not start. It will charge and start. It will run and not start.
Looking at it from the 2 battery posts...
If you have a reasonably used battery that is properly filled with good battery cables...
...and the battery will not start the engine, the battery is the problem.
...and the battery will not recharge to start the engine, the battery is bad.
...and the battery will recharge to start the engine, the battery is good.
...but the good battery will not start the engine after running, the engine is the problem.
...but the good battery will not start the engine after not running, the bike is the problem.
A manual is a couple extra volts all by itself