The battery indicator in my D5100 has 3 'bars' but fails to operate shortly after reaching 2 bars. My experience is;
Three bars indicates battery is good
Two bars indicates battery is going to fail imminently
One bar doesn't figure at all!
This weekends experience. A check on the battery life shows 2 bars so I don't bother recharging for the next day. Next day take a couple of shots and the camera fails to focus and the battery indicator flashes. Remove the battery, heat up in my hand and replace. Two bars showing and I manage another 15 shots before total failure.
Do I have a faulty battery? Is there any way to check this?
#1. "RE: D5100 battery indicator" | In response to Reply # 0jec6613 Registered since 12th Feb 2013Mon 18-Feb-13 04:53 PM
This happens to mine when the camera is cold. The battery meter reads out from the SBS chip on the battery (the battery has a monitoring processor inside of it), but the low battery indicator is triggered by voltage.
To see if your battery is faulty, I'd have to know how many shots overall you got - if it's over 500 using CIPA type conditions (no live view, just stills), your battery is more than okay.
#2. "RE: D5100 battery indicator" | In response to Reply # 0MEMcD Nikonian since 24th Dec 2007Mon 18-Feb-13 08:24 PM
It is normal for batteries to lose power when they are exposed to cold temperatures.
Batteries rely on chemical reactions to produce electrical energy. As the temperature decreases the chemical reaction slows down thus reducing the energy available to power your camera. In cold temperatures, always keep a spare battery in an inside pocket. When the one in the camera starts loosing power switch them out.
Good Luck and Enjoy your Nikons!