This might be something to try ... use one of the newer PAR36 LED lamps instead of the incan. Quite a few available on different sites, I bought a pair on eBay & each draws only 12 watts (contains 6 LEDs, each one draws 2 watts). They're brighter than the 50 watt incans I used before but not as bright as a 100 watt bulb.
Battery life would be very long.
Do you have a lamp description or seller name? How much did you pay for the LED PAR36 lamp?
The ones I saw on eBay were a little too much $$ for me to justify trying.
Thanks!