Hi there, first post.

Just last night, my Instinct started powering off, despite having a fully charged batter.  I popped in my other battery, also fully charged, but it still would not power on.  I plugged it into the charger, and it would power on then, but only for a few minutes before powering off.  I left the phone off and charging for about an hour, and the spare battery charging for the same time.  After they had charged for an hour, I tried the phone again.  It would still not power on off the charger.  I tried the spare battery, same result.

I went to the Sprint store nearby, and duplicated the problem there.  They seemed to think both batteries went bad at the same time, and replaced them, along with the spare charger. My Instinct was fine the rest of the night, and  I left one battery charging in the car overnight, and had the phone on the desk charger overnight.

Fast-forward to 30 minutes ago, I'm at work and my phone is dead again - it will only power up on the charger.  I have the USB charger here, and I went out to the car and got the spare battery.  Currently the phone is working on the spare battery, and the other battery is on the charger, I got a green light in just about 5 minutes, so I know the battery is not the issue. 

Has anyone else experienced a similar issue?  Any advice to offer?  I've been a Sprint customer for 6 years now, I've been very pleased with their service and support.