nicd and nimh have "self discharge" and will lose a large percentage of charge just sitting there.
great for an electric bike with big currrent demands, some idle time, big current demands, etc. or cordless power tools, where they can go on a charger every night.
theyre easily charged.
and discharged
this is important.
lithium polymer and ion batteries have huuuuge current capacities, with pretty good shelf life, but have very complicated wiring systems because each cell in a pack needs to be individually charged (or balanced) else they EXPLODE!!!
(poly more so than ion)
so as the voltage goes up, with 3.7 volts per cell, the wiring and charging gets proportionately harder...
same time, you only need half as many cells as a nickel based type of the same voltage.
(and really, even nickel packs should be balanced...they never are)
lithium being the third element is extremely light as well.
the lithium types also cost more.
they also cant be discharged beyond a certain point so require a fancy expensive speed control with BEC, otherwise, you guessed it...they EXPLODE!!!
for now id stick with nickel based types. cheap, easy, do the job and are a good entry level product...
sla will only bring you tears in the long run
may seem cheaper but they add up after being replaced a few times...
sla despise being discharged too quickly, they despise being charged too quickly, they just dont cope with huge current demands.
yep. chemistry
zinc, copper and salt water
thats the way to do it