Rapid BAttery Charger

[GregAndrew]

If I remember correctly, when the voltage is held constant, then amps = watts/volts. So a 5 watt solar charger is only going to give you 5/12 amps per hour of charge. So 12 hours charging time will produce 5 amps. Might need something in the 12 -15 watt range to keep that size battery charged (with the spare battery charging all day).

[jbm]

Originally Posted by GregAndrew

If I remember correctly, when the voltage is held constant, then amps = watts/volts. So a 5 watt solar charger is only going to give you 5/12 amps per hour of charge. So 12 hours charging time will produce 5 amps. Might need something in the 12 -15 watt range to keep that size battery charged (with the spare battery charging all day).

You remember correctly. And that 5W rating is generous. You'll probably only get about 0.3 amps out of it on a sunny day.

You can do the jumper cable thing, but have the vehicle running. And again, monitor that battery, watch for heat or gassing.