I dunno about juice going stale. I have some juice that's months old and it's still the same as it ever was.
Batteries can go sour though. If you have a multi-tester you could check the voltage. There are even mods that will check the voltage under load.
From my experience, my Joye eGo's and Rivas have lasted a really long time, but like any battery, your mileage may vary. I would suggest testing the voltage, and also consider trying a new charger. It's a bit difficult to troubleshoot this without more info, but if you can provide a bit more, someone will probably have a good idea as to what the issue is.