Except for the MAG-TAC flashlight that runs on lithium CR123 batteries, all of Maglite non-rechargeable LED flashlights operate on AAA, AA, C, or D-cell batteries. All of our published ANSI-standard performance data (Light Output, Beam Distance, Peak Beam Candlepower, and Run-Time) are based on testing with alkaline batteries; and when we ship these flashlights with batteries, the batteries we include with them are alkaline. We do this because the designs of these flashlights are optimized for use with (non-rechargeable) alkaline batteries. Alkaline AAA, AA, C, and D batteries standardly have a nominal output of 1.5 volts. NiMH rechargeable batteries in these sizes typically have a somewhat lower nominal output (1.2 volts). Also, the discharge curves of NiMH batteries typically differ from those of alkaline batteries – so the two battery types may behave differently under load. That said, the flashlights will operate with NiMH rechargeables, and the use of NiMH rechargeables will not harm the circuitry nor otherwise damage the flashlights in any way. You should not, however, expect the flashlights’ performance to be consistent with our published ANSI data if they are operated with rechargeable batteries. (For example, ANSI Light Output may be lower, and/or ANSI Run Time may be shorter with rechargeable batteries.) The degree of difference is hard to predict. We have noted variations in the quality of NiMH rechargeable batteries on the market, and if you choose the best-quality NiMH batteries you might find that any performance shortfall is, for your purposes, not meaningful. Bottom line, if you are willing to tolerate a possibly significant decline in flashlight performance, there is no reason you can’t substitute rechargeable NiMH batteries for (non-rechargeable) alkalines.