l live camping/ off the grid
so pocket sized headlamps are crucial to my life style
l really like the formfactor/symplicty of my tackktica but AAA batteries suck even the energizer Li-FeS2 ones

l want to modify my head lamp to take 10440 li-po cells
cuz their betterer -- more stable, rechargeable etc

stock it runs on 3 AAA in series
for a nominal voltage of 4.5v

the li-po cells l want to replace them with
have a nominal voltage of 3.7 volts

options l can think of are
1 -3 3.7v cells (in parallel)

2-3 3.7v cells in series with a voltage regulator...

don't know which is the better option

also l want to charge the new batteries in the headlamp
can these cells be charged parallel?

l doubt any one will see this
but if you do please help