On the left is a 100 amp hour Bilthard Lithium Battery. Batteries can be purchased on Amazon for about $150. They last over 10 years and are safe - with no gases given off - no liquid leakage. On the right - is an inverter. It converts the 12 volt DC power to 120 volt AC power. Just 2 wires.
I use this setup to power our refrigerator - several lights - my CPAP machine - and charge our iPhones. It even has USB plugs for Applewatches and computers.
In a test I was even able to power a small window air conditioner but only for a couple hours.
You eventually must charge the battery with a lithium battery charger - about $50. The little blue gauge on the inverter tells you what voltage is left. 13.5 volts is full charge. It tells you also how many watts you are drawing. you can see the two USB ports.
I used to have this battery in my motor home - but I replaced that with a 300 amp hours battery that cost $350.
