http://www.nikonchat.com/nikon-coolpix-nimh/

Nikon Coolpix L100 battery question?
we have a nikon coolpix camera that says “battery exhausted” when we turn it on. it’s got brand new, fully charged NiMh rechargeable batteries in it, yet it still says that. are we using the wrong batteries for this camera, or is it an electrical defect inside? any help would be great.
Originally the L100 didnt accept NIMH batteries. It only accepted alkaline or lithium. In June 2009 Niknon came out with rechargeable NIMH batteries and a charger for use with the L100. It could also accept other brands of AA NIMH rechargeable batteries.
Owners have to download an L100 firmware update and install the new firmware into the camera or it will not accept rechargeable NIMH batteries. Have you upgraded your firmware for the switch to NIMH rechargeables?
Below are links to the original L100 specs including battery specs, a Nikon press release announcing the inclusion of NIMH batteries and the Nikon page to start your firmware upgrade.
nikon coolpix l20 10MP Digital Camera w/3.6x Optical Zoom (Deep Red) 4GB BigVALUEInc Accessory Saver