Seems like this is better than adding a 12v battery.
The new Gem taps into a 12v battery.
This is a 20a balancer. You can charge all batteries from a single 12v charger or maintainer.
48v, but 72v also available.
The 72v version.
This will let you use mismatched batteries. Helpful if one battery dies.
Charge all with a 12v battery charger.
At 20amp rate it should also allow use of a 24v or 36v inverter.
That is pretty cool!!!