Low Battery when not

First make sure you are using either brand new or fully charged re-chargeable batteries. If there the issue persists, there was a firmware update for the camera to resolve an issue similar to this, and you may need to get the update. To check what version you have, do the following:

-turn the camera off
-turn the top dial to SETUP
-turn the camera on while holding down the MENU button

A splash screen will display and it was say 'E3100 v1.X' in the bottom right side of the screen. If it says v1.1 or v1.2, you will need to upgrade the firmware. For instructions on doing this, please see:

Title: Coolpix 3100 Firmware Update 1.3 - Windows
URL: http://support.nikontech.com/cgi-bin/nikonusa.cfg/php/enduser/std_adp.php?p_faqid=13030&p_created=1102934617

Title: Coolpix 3100 Firmware Update 1.3 - Macintosh
URL: http://support.nikontech.com/cgi-bin/nikonusa.cfg/php/enduser/std_adp.php?p_faqid=13031&p_created=1102934414

If it says v1.3, then you already have the update and your camera may need to be repaired. For repair information, please see:

I got this from Nikon Tech support and it worked.
First make sure you are using either brand new or fully charged re-chargeable batteries. If the issue persists, there was a firmware update for the camera to resolve an issue similar to this, and you may need to get the update. To check what version you have, do the following:

-turn the camera off
-turn the top dial to SETUP
-turn the camera on while holding down the MENU button

A splash screen will display and it was say 'E3100 v1.X' in the bottom right side of the screen. If it says v1.1 or v1.2, you will need to upgrade the firmware. For instructions on doing this, please see:

Title: Coolpix 3100 Firmware Update 1.3 - Windows
URL: http://support.nikontech.com/cgi-bin/nikonusa.cfg/php/enduser/std_adp.php?p_faqid=13030&p_created=1102934617

Title: Coolpix 3100 Firmware Update 1.3 - Macintosh
URL: http://support.nikontech.com/cgi-bin/nikonusa.cfg/php/enduser/std_adp.php?p_faqid=13031&p_created=1102934414

If it says v1.3, then you already have the update and your camera may need to be repaired.

If you are using alkalines, this will always happen. You need to use rechargeables, or special high current disposables, eg "Oxyride".

A good solution for this camera is to use a single CRV-3 disposable lithium batteries. The battery life is long and they are light weight too.