G1 keeps turning off by itself

remove the battary make the battary clean and fix the battary properly and charge the battary if it will not effect then give the phone to a samsung delear

check your battary and battery conector

You can try to do a hard reset on the phone. If that keeps happening after that. Then you have a hardware issue.

Heres what to do. Take the battery out and put it back in. You will want to hold both the home button as well as the power button when you power the phone back on. Keep holding these buttons until a screen pops up with a triangle on it and a phone below. Wait 5-10 seconds, and then press the home and power buttons together again. This will bring up the restore options to factory restore the phone. If this does not work, you will need to contact T-Mobile regarding the phone issues.

If it keeps rebooting itself at the G1 and Android screen, you might want to factory reset the phone and clear all the data as there may be a virus. To do this, when turning on the phone, hold the home button and the power button even while the G1 screen comes up. Keep holding these until an image with a triangle comes up. You will then wait 5-10 seconds, and press the home and power button again together. This will bring up the OS screen, and provide you 4 options. One of these options is to wipe and restore to factory. Do this and your phone should work fine after you reboot again.

the phone battary needs a replacement

Have you tried recalibrating the battery? To do this you use the phone until it completely runs out of battery and switches itself off. Make sure it has completely run out by continuing to turn it back on until nothing happens except a red LED coming on. Then charge it while it's off until the green LED has been on for 2 hours. Hopefully this will improve your battery life.

Have you tried a reset using the hardware buttons? To perform this, you need to turn off the phone first. While it is off, press and hold the home key and the power key at the same time. Keep holding the buttons until you see a screen with a triangle and an exclamation point in the middle. Once you see the triangle, let go of the buttons and open the keyboard. Press ALT+W at the same time, and the phone should reset.

You are going to have to ty a hard reset. Don't worry about things being deleted from the phone, as your phone auto syncs with Gmail when you enter your account info again.

To hard reset...turn the phone on while holding home and back. Follow on screen prompt.

If that doesn't work try..

Hold home and power buttons
once phone is on, open keyboard and hold alt first + w

check backup battary