My bike will start up and idle perfectly fine for an hour but if I shut it off and try to start it again it won't start. When the bike is idling the battery is being charged at 12.1v and when it's revved up to 4k it's about 13-14v. This seems right but why won't it re-start if I just leave it there idling?

It will start up fine if I ride it normally but shouldn't it be charging more than 12.1v at idle?

My battery is a Walmart battery that's almost 5 years old so I think it's going bad but was wondering what everyone else thinks.

 

My bike does the same thing. If I'm going to be idling it for a while, I set the idle screw up to 3k and the voltage rises to 14v so it charges instead of draining. Probably not ideal, but it works for me.

 

By design, while at proper idle RPM the battery doesn't charge. So if you have a weaker battery and let the bike idle for an hour, you may experience a flat battery.