most 3AAA lights are designed for primaries (alkaline or heavy duty) and the runtime is already increased by the batteries unable to provide the current the led can take. to put batteries able to provide more current will most likely decrease runtime while increasing output. The only way to change that is to change the circuitry either adding a resistor into it to throttle the current down more or a regulator. If it has a high power led in it I would just try lithium AAA primaries and be content you will have less runtime but worry less about the batteries.