Battery recharging performance varies pretty widely by vehicle, but it is likely most people vastly overestimate the alternator's contribution.
I have 3 batteries in my camper van, solar and a battery monitor which reads alternator amps. When my batteries are within 20% of fully charged, the alternator's contribution is pathetic. Basically my 130 watt solar (7.39 amps)panel in good sun is more effective than my alternator when the batteries are above 80%. Upgraded wiring and high RPM's have little or no effect on increasing alternator recharging in that state of charge zone, much to my chagrin.
It's always better to plug in a battery to the grid (or strong solar) rather than relying on the alternator to top it off. I try to meet the charging specs listed by my battery manufacturer, which is 20 amps at 14.5 volts. When I do so, they hold more voltage under use than when recharged slower. But these are true deep cycle batteries, a different animal than a starting battery.
I have 3 batteries in my camper van, solar and a battery monitor which reads alternator amps. When my batteries are within 20% of fully charged, the alternator's contribution is pathetic. Basically my 130 watt solar (7.39 amps)panel in good sun is more effective than my alternator when the batteries are above 80%. Upgraded wiring and high RPM's have little or no effect on increasing alternator recharging in that state of charge zone, much to my chagrin.
It's always better to plug in a battery to the grid (or strong solar) rather than relying on the alternator to top it off. I try to meet the charging specs listed by my battery manufacturer, which is 20 amps at 14.5 volts. When I do so, they hold more voltage under use than when recharged slower. But these are true deep cycle batteries, a different animal than a starting battery.
