Most all automotive alternators/generators are designed to produce their
maximum amperage at highway/normal crusing speed, which is not really the
speed of the vehicle, but the engine rpms, which for 90% of vehicles on the
roadway is 1,800-2,200 rpm. Anything below this engine rpm, and the output
(amperage) drops off exponentially. An automotive alternator is not meant to
charge an automotive battery, merely to maintain a somewhat constant state
of charge to a properly charged battery, with the factory electrical components
originally equipped to that vehicle, operating at normal loads. An aftermarket
battery is (almost) always superior to a factory battery in all respects, yes,
(dry load, cold cranking amps, or"cca", drop-down load, reserve capacity, etc...)
but you have to have a charging system, or as we were told to call it
at the Automotive College that I graduated from, a "battery maintenance device",
or something like that, capable of maintaining that battery at its specified state
of charge, or "specific gravity" (more on this later!). If you have an underdrive
pulley system, aftermarket accessories, and tend to use your "battery maintenance
device" (alternator) below specified rpms, such as idling or low speed driving, with
aftermarket stereos and hella lights, winches, etc..., you are just asking for
a dead battery. If you are serious about this, you should really consider upgrading
your entire electrical system (alternator, battery, cables, switches and relays,
and don't forget about good, solid grounds!). if you're gonna do it, do it right!!!
