We’ve already got a large solar panel on the van attached to a 100Ah battery. The problem is that we don’t always know how full the battery is. You can roughly guess the state of the battery by looking at the voltage, but it doesn’t always give a clear picture, especially when your solar charger is trying to trickle in power all the time.
A more accurate way is to use a battery monitor that measures both voltage and the current going in and out of the battery. With some maths and some clever algorithms, they can work out how many amp-hours you’ve got left. Even better, they can record your daily use, estimate how long the battery will last at the current use rate, and estimate how long before you reach full charge.
After doing some research, I got us a Victron BMV 712:
The kit is pretty comprehensive, but what it does assume is that you’ll be flush mounting the circular display, which wasn’t an option for me when it’s going on an outside wall. Victron do sell a surface mount box, but it’s not cheap!
Instead I practiced my CAD skills and 3d printed myself my own box.
I’ve uploaded the design to Thingiverse if you want to print your own.