Magnum ME-BMK Battery Monitor with shunt for sale that I bought but never installed. It's brand new in the box.
Comes with manual and everything you'll need to get it installed. You just have to have an ME-RC50 or ME-ARC50 remote or an ME-RTR router in order to see the monitored information. The BMK plugs into the "network" port on your inverter with the included cable or can be plugged into the "remote" port with included splitter on inverters that don't have a dedicated network port (MMS series). An email with Magnum confirmed that there is full functionality either way.
Additional info here: https://www.magnum-dimensions.com/battery-monitor-kit
$120 shipped. I can take Paypal for payment.