Phone boots, but then turns off

[fuznuts]

Hey there guys. I am once again in need of your assistance (maybe sprint should pay you instead of its ignorant employees...

Well anyway, I bought a second battery for my htc touch from a website called the "cellphoneshop". I use an external charger for it so I can just turn my phone off, replace the used one with a fully charged one (which is only about half the thickness of the stock one).

This was working fine for a few days. Even though the secondary battery only has about 50% of the original battery's charge-life. But recently when I put the battery in it allows me to boot, and goes all the way to the "today" screen. But about 10 seconds after the opening sound, the phone just shuts off. No long shut-down process like it is supposed to do, but just like i took the battery out...

I would say this is a battery issue, but sometimes it still works. The area where the main screen shows your batteries charge has an exclamation point and no battery life shown, but that has always been the case.

I am running Juicy's Rom with very few other applications.

Any thoughts?