6100:keeps turning itself off, battery is brand new...

My dh has a 6100, he is VERY rough on cell phones because of the work he does, but last month he started having a problem with it just turning itself off. We went and spent $40 on a new battery, thinking that was cheaper than a new phone( we dont' have the insurance, like we should). It worked just fine with the new battery for a few weeks and then this week it started doing it again. Does anyone know what this might be and /or how to fix it. We have to keep these phones until January. He keeps missing calls when it turns off, he uses it for business( farm) but he needs something that will be durable. When we got these phones, the second, I kid you not, he feel off of a tractor and hit on the new phone cracked the outside screen , but it still works just fine. He has dropped it numerous times but never in the water, I told him no matter new phones we get, we are getting the insurance this time.
But I need to know if there is any way we can get this problem taken care of before January, cause we know that we can't get anything done until then. We don't want to pay retail for a new phone for him. Like I said, he uses this thing exclusively for business and we need the business right now!!

Try to find a used phone somewhere. Maybe one of your friends has an old one that can still be activated. Or give him your phone, and you deal with the phone shutting off. It's probably just been knocked around too much. Phones are electronics not bricks.

Have you tried going into the display settings and turning down the backlight settings? This may help save battery time.

I don't think battery life is the problem. I think that the phone shutting itself off is the problem.

Does it complain about low battery just before shutting off? Sounds to me like he's over discharging the lithium battery and killing it. I would suggest he charge the phone every night. If the voltage drops below a certain point, the battery will not hold a charge anymore. The belief that you have to discharge your battery completely before charging again is a myth from the Ni-cad days. If the battery says "lithium" somewhere on it, always keep it charged. Especially when storing it/not using a battery for long periods of time.

Likewise, never store a modern rechargeable battery in a refrigerator. The condensation when removing it from the cold environment could cause it to have a high resistance short and discharge.

All of this goes for lithium laptop batteries too.

Does he carry his phone/spare battery in the same pocket with his keys? that could short out contacts on the bottom of the phone/battery causing bad things to happen. If he is, get him a good holster.

My phone cut off like that when I made my ower slient ringer for the camera...
Any changes made like that?
change back.