solar charging tool battery

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New member
May 18, 2023
I want to charge an 18v lithium tool battery 3AH with a 10 watt panel. The panel output is Voc 19.5 v and Isc is about .5 (1/2) amps.
Would the bms in the tool battery prevent overcharging and act like a simple solar controller? The panel output seems to be well matched to this battery.
But, with lithium there is some concern.
Voc means no load. Once you apply a load, it's gonna drop. What's the panels Vmp? That's going to be roughly what the voltage will be when a load is applied.

To charge the 18v batter, you'll need some sort of charge controller, and/or a second panel in series, and/or 1 higher Vmp panel.

Alternatively, there are some charge controllers out there, like the MPT-7210, which are boost controllers and can raise panel voltage to charge a battery at a higher voltage. So the panel you have currently, plus the MPT-7210 set to your battery's max charging voltage, would work. You'll have to check what your specific battery's max charge voltage is, and set the controller to accomodate.