6v photovoltaic panel is normally equipped with 3.2v lithium iron phosphate battery, or ternary lithium battery 3.7V, 18650 lithium battery can also be used, you can also use 3 photovoltaic panels in series to form 18v, you can charge 12v battery. If the current is large, and the connection method plus the series connection method, so that the current is large and the voltage is large
Normally, two parallel 1500MA 18650 can be charged, remember to add lithium battery protection board, otherwise overvoltage will charge the battery.