These guns were basically bought for my son but never used outside the garden and have sat for over a year doing nothing. That was because they both stopped working.
I have zero knowledge on these guns and have no idea what a mosfit is. Sorry.
As for charger. See attached photo. Again, no idea about the setting on it.
But last night I put the batteries on charge and 12 hrs later the green lights were still flashing, meaning not charged.