All the product manuals and literature out there talk about the charger having three (sometimes four) "stages" - bulk, absorption and float (sometimes by different names). But here is the piece that I am puzzling about. For DC circuits, V=IR. The charger cannot change that rule and "R" is the internal resistance of the battery, which increases as the battery becomes more fully charged. The charger cannot control the "R" value - that is determined by the battery. So when the literature says "the charger maintains the voltage and reduces the current" this simply cannot be true - the charger cannot control *both* the voltage and the current at the same time. The charger can set a target voltage, in which case the resistance of the battery determines the current. Or the charger can set a target current, in which case the resistance of the battery determines the voltage.
So my question is this - is this three stage process simply a matter of the charger trying to maintain a particular voltage level without exceeding some amperage output and the varying resistance of the battery governs whether we are current-limited (in which case the voltage drops and we are in the "bulk" stage) or voltage-limited (in which case the current drops and we are in the "absorption" stage). The "bulk" stage simply reflects the fact that the resistance of the battery is low enough that the current draw exceeds what the charger can deliver, and the "absorption" stage simply reflects the fact that the battery's resistance has become high enough that the charger can now deliver enough current to obtain the fixed target voltage. The charger isn't really doing anything different in these two "stages" - it just wants to output a certain voltage but it has a limit on how much current it can deliver. The charger's target voltage and current limit do not vary - the only piece that varies is the resistance of the battery.
I could see the charger having two stages - stage 1 is try to obtain a target voltage with an amperage limit and stage 2 is once we are at the target voltage and the current has dropped to a certain point, then the charger decides to lower the target voltage (this would be the float stage). So I can see a charger having two stages of operation (essentially two different target voltages - one for the bulk/absorption phases of the battery and a second, lower target voltage once we hit the first target voltage and the current drops below some threshold). But I do not see the charger doing anything different during the bulk and absorption phases - the observed behavior in terms of varying voltages and currents is the result of the battery's resistance changing and the charger having a limit on how much current it can source.
So my question is this - is this three stage process simply a matter of the charger trying to maintain a particular voltage level without exceeding some amperage output and the varying resistance of the battery governs whether we are current-limited (in which case the voltage drops and we are in the "bulk" stage) or voltage-limited (in which case the current drops and we are in the "absorption" stage). The "bulk" stage simply reflects the fact that the resistance of the battery is low enough that the current draw exceeds what the charger can deliver, and the "absorption" stage simply reflects the fact that the battery's resistance has become high enough that the charger can now deliver enough current to obtain the fixed target voltage. The charger isn't really doing anything different in these two "stages" - it just wants to output a certain voltage but it has a limit on how much current it can deliver. The charger's target voltage and current limit do not vary - the only piece that varies is the resistance of the battery.
I could see the charger having two stages - stage 1 is try to obtain a target voltage with an amperage limit and stage 2 is once we are at the target voltage and the current has dropped to a certain point, then the charger decides to lower the target voltage (this would be the float stage). So I can see a charger having two stages of operation (essentially two different target voltages - one for the bulk/absorption phases of the battery and a second, lower target voltage once we hit the first target voltage and the current drops below some threshold). But I do not see the charger doing anything different during the bulk and absorption phases - the observed behavior in terms of varying voltages and currents is the result of the battery's resistance changing and the charger having a limit on how much current it can source.