Some info.....this might be gobblgiegook for some, but could be manner from heaven for others........
Batteries store 'CHARGE'.The bigger the battery, the more charge it can store. Charge is measured in 'Coulombs' or 'AMP-HOURS' (amps x hours).
Because of the chemistry inside the battery, electrons (charge) that were in the acid and the lead plates are moved, and stored (held) in the opposing Lead plates.
This 'DIFFERENCE' in charge between opposing plates can be thought of as the 'electrical pressure or force' or 'VOLTAGE'. Voltage is 'the ammount of ENERGY on each unit of CHARGE' (Joules per coulomb)
If something conductive is connected accross the battery terminals, the charge (electrons) will flow from the high pressure (high voltage) terminal to the low one. This flow of charge is the 'CURRENT' and measured in amps. Current is the 'RATE of FLOW' of charge. (coulombs per seccond)
POWER is 'voltage multiplied by the current' and tells you the 'RATE that you are converting ENERGY' (joules per seccond) from electrical energy in to all of the other types of energy.
The difficulty with measuring power is that; in a car, energy is being converted in various directions at different times. when the engine is off it is from battery to the load. When the engine starts the battery becomes part of the load supplied by the alternator...untill it is topped up..
Voltage can be measured from 'ACCROSS' the battery terminals easily (Arnolds method will be the best for this) this can give you usefull info on the how healthy your battery and alternator are.
But Current 'THROUGH' the circuits is a real difficulty ( Ed explained why)
Hope this description is usefull for some....sorry for spellings as usual.....;-S
