Does this high side n-ch mosfet bootstrap circuit work?
Circuit 1: Both fets turn ON when Q3 turn OFF, the state stays until leak currents spoil it. But turning Q3 for a short time refreshes. 

Turning Q3 OFF turns both fets ON also when the panel outputs less than 10V but the battery has 10V. This can be an unwanted thing, if nothing prevents the discharging from the battery.

Removing R2 prevents charging C1. But you can use a switching transistor in series with R2 to keep the unwanted current duration short.

Do simulations for the optimization.

Circuit 2: It works. When Q3 is ON (=conductive), both mosfets have negative gate-channel voltage and are OFF. When Q3 is OFF, the resistor pulls the gates about 10V above anything in the channels of the fets and this makes both fets conductive. This can also be dangerous, if the fets do not stand +20V gate to channel voltage.

A suggestion: If you want to use N-mosfet because you have them, you can put it to the minus wire and avoid the need of any voltage boosting trickery to get the gate voltage. It is having the plus side = GND