I think it's more about the current output - rechargeables in general don't supply as much current as standard batteries.its to do with the voletage output. Apparently rechargeables have a lower voltage and so should be avoided, the Mah i just how long they will run at that voltage, so obviously get the biggest you can. it's possible to run off two 9Vs so search for 9V halo mods on ebay / PBN / something