I have a 2007 Suzuki Boulevard C50.

After charging the battery on a trickle charger the bike will only run for 20 minutes or so then it shuts off.

I was running it on the highway and each time it shut off was when I got of onto an exit ramp or just slow traffic. Not sure if this was a coincidence. The first time it happened I was able to push it to a p-lot and wait for my wife to come by with jumper cables. I put it on the jumper cables for about 20 minutes or so and then tried to make it back home. It ran fine until I hit some stop and go traffic and it shut down again. Hooked it back up to the jumpers cables and waited another 20 minutes then tried to finish getting home. It once again ran fine and even had to stop at a couple of traffic lights and it did not shut-off and I made it home. The last leg where I made it home was only a few miles.
I replaced the rectifier and had the battery checked out at local Advanced Auto and it was good.
I put my volt meter on the battery and got readings in the high 12's. I started the bike and and volt meter then read around 14. So it seems like it is getting a charge so why is it shutting off after about 20 minutes of riding? Thanks for the help.

 

Did you confirm that the terminal connections are not loose?
Sounds simple but intermittent contact could be an issue.