iPhone Shuts off randomly, goes to apple screen
So I have an Iphone 3gs 32gb. I think it's about 2.5 years old ( I got it off a friend) initially I had a hard time jailbreaking it and unlocking the phone because when I put in my simcard it would give me a no service/searching.
Not sure what my friend did to unlock it but it works perfectly. But now it would randomly turn off and when I do a hard reset (home button and power button pressed at the same time) it'd take me to the apple logo. Occasionally when I plug my iphone in to a power source, a yellow screen would show. However I am able to recover out of the apple logo page/yellow screen when I plug my iphone into my computer or a wall-charger. But when I take it out of the charger 1-5 minutes later (depending upon the percentage of battery I am in) it would crash again, reboot to the apple screen and then I'd have to plug it into a powersource in order to get out of the apple logo screen.
Anyone knows what's wrong? Is it a battery problem? I'm starting to believe it is, it's crashing and rebooting when I'm around 80% battery and doing so more often and at shorter period of time as my battery life decreases to 70% until to the point at 60% where once I take it out of my charger (just after recovering form the last random shut down)it'l just automatically shuts down.