(Drivers side rear)
It's not until you use something that you learn how good your design works. Last year i was working with concepts and I knew I needed a house battery, or batteries. I also knew that I wanted to use existing Prius space and my house batteries would be 12 volt gel cells.
Then the question was how to charge the gel cells. There is a company that sells 12 volt gel cell chargers but this wasn't the path I took as I also wanted to be able to charge and condition my Prius 12 volt battery.
My decision was the Battery Minder's multi chemistry battery charger as it allowed me the ability to switch and charge either the house battery or the Prius 12 volt battery. (Charger can be selected to charge AGM [Prius 12 volt battery], lead acid 12 volt wet cells, and 12 volt gel cells)
With time running out last year I left with the ability to have a cord from the house battery and another to the Prius 12 volt battery and had to plug and unplug the cables as I chose to charge one or the other. Mostly I charged the house batteries.
I had to plug and unplug even the house battery as the charger design is that once a battery is plugged into the battery charger the power from the battery is exchanged with the charger and the charger lights are on. That meant that as long as I was charging all was good but once I stopped charging the battery was feeding the display of the charger draining the house batteries.
This resulted in two problemsat year I wanted to solve.
The solution was a double pole / double throw switch / with a center position (on/off/on) where there is no center connection.
I selected this switch with lights but the lights can't be used as the outputs of the switch are batteries and not powering a load. The power back feeds and keeps the lights lit even when the switch is in the off position.
I dressed the switch with some old connectors to match the charger cables.
I have the charger mounted the on the drivers side rear.
I selected the spot and used the vibrating saw to cut the switch hole. Then I put the switch in and cabled it.
The switch on the upper left supplies power from the house batteries to the panel on the right. The center is the voltage monitor and the left is the dual USB charger and the right is a 12 volt car outlet.
Here is the charger and wiring to and from the two batteries as well as the power distribution for the house batteries.
When not on shore power I charge the house batteries through a pure sine wave 400 watt inverter from the Prius 12 volt battery on the opposite side rear on the Prius.