Motorola V265 / V266 / V276

This has just started today. I'll be sitting here and my phone will start buzzing, like the power-up/power-down vibrate, then the inside screen goes dark. It's hard to get it to power down, and sometimes when I try I just get into a pattern of recurrent buzzing, going dark, etc., like it's trying to reboot itself.

Is my unit toast? Could it be the battery?

TIA