I'm having the same problem. Wife was playing a game yesterday for 3 or 4 hours with screen at 100% and got a 15% battery warning, but I had to wait for her to finish (20 minutes) before plugging it in. Using her mot charger (different phone, but worked before), it quickly charged to 40%, but seemed to stay at 40% for some time before I unplugged it to go for a 2 hour walk with the gps on to track our route.
Received 15% warning sound before arriving home and quickly plugged it in again, but phone never charged. Pulled the battery and replaced and still would not charge. Saw 15%, then 10%, then the battery low prompt kept coming up like once a second so shut the phone down and let it charge all night. This morning, never saw more than the moto logo when trying to power it up.
Plugged into the usb on the computer now, no tone, Windows doesn't show it plugged in and can't power up the phone. Did have a green LED light on the phone for a bit, but playing with the power button to try to boot turned that off and it's like a brick now.
I suspect I'll have to see if Verizon is open today (I'm out of town). Had an extended battery on BO using the coupon code. If they're going to give me a replacement battery, I'd rather it go toward the extended battery, but not too keen on paying $50.
I wonder what happens if I borrow a coworker's X battery long enough to power up the phone and while connected to a charger or usb, hot swap with my batteries, if it'll charge then? I've only seen a 15% warning once and didn't have trouble like this.