nope 12V din ang LEd only that it consumes .5-2 watts while generating the same brightness..but not the same illumination. LEDs that can provide illumination are much expensive,e...

and no, size and pulley of the alternator is the key factor--kung malaki masyado ang dimension ng alternator--di mo mafifit ng maayos sa engine...pero unsually, 90AH alternators are stock in some engines, especially in diesels, kaya merong makukuha,e...pulley is the key factor--pag lumaki sa stock pulley mo, may prob ka, kung masyadong lumiit, prob din, dapat pareho lang ng original..

at kung lesser alternator, lesser din ang power..smaller alternator gives smaller electricity--just like a small motor which can give only accomodate a small load...

to compute--dapat total AH mo should not be greater or equal to rated load ng alternator mo, kung di, ddrain mo battery mo..give atleast 50-60% allowance so that the alternator can charge your battery...