I'd also forget the coil. The coil may or may not work but you need to be careful when connecting things to your batteries. I dont recall what batteries you are using but wet batteries gas, so creating a spark can cause an explosion of plastic shrapnel and acid. Any coils,chargers or other loads need to be connected to a fuse and switch and not make and break the load at the battery.
I think you would like a trimetric battery monitor. You would be able to see pretty much everything that is going on and see a history log too. The trimetric is very popular but others also like the Victron and could tell you about it. The trimetric can also be easily connected to Bogart engineering 30 amp solar controller.