Pure Sine Wave Power Inverter
So you've been charging your batteries (in a number of ways, for example with solar or a voltage-sensitive relay) and you are now to use that power for your appliances: just like you would in a house, you need an inverter to convert that power from a DC current to an AC current.
This particular inverter is affordable and reliable, it allows you to plug appliances straight into it, which is great if you want to save the hassle of wiring in extra plug sockets around the van. It also tells you your current battery levels. You don't need an inverter if you only plan to charge things through USB ports, but we often find there is something that needs to be plugged in.
The only downfall of inverters is that they consume energy from the battery to convert that power, so you do have some energy loss. This product also comes with a switch which you could install somewhere that is more accessible in your van.