I have been looking at portable solar panels lately and found one that I think would work wonderfully with a 3.7 Pass Through, any thoughts?
Maximum Solar Cell Wattage 18W
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Highest efficiency commercially available, monocrystalline solar cell with silicon nitride, anti-reflective coating (125x125mm, 2.6W max)...
There are some chargers that have 12V ports (Trustfire) so you can use a DC source to charge on the go. You could possibly use a 12V solar panel plugged in to the charger to charge the batteries. This is purely speculation that a small panel would actually put out enough power to run the charger. I suppose I could try it with mine and see if it works... have to dig out my panel and see if I have a connector that will fit the trustfire charger.