Ignore the light in dash and add a analog round simple volt meter to dash that will show you where your battery pack voltage is?
I drill the 2" hole where light is mounted now and run 2 16-18 guage wires from meter to the plus and minus sides of battery pack along with a 5 amp fuse for protection. This is easiest way to add meter and will be on whenever you want to see charge of pack ( it can stay on all the time as draw is nearly nothing )