Couple of concerns I noticed over the weekend

The ONLY time you can get an accurate reading of battery state of charge is when there has been NO drain placed on the batteries and NO current put back in them, for a fairly lengthy period of time. If you check them WITH a drain on them you will ALWAYS get a lower reading than their state. If you check them with current being put INTO them you will get a reading of their SURFACE charge which will show a higher state of charge than you actually have. If you're INTERESTED i knowing how your batteries are doing forget the useless wall mount system and use a volt meeter ONLY when it's appropriate and consistent with getting an accurate reading. For what it's worth though, you can NEVER measure your battery staying power by a TIME factor, it will always depend on how much POWER you remove from them and how well charged they were before beginning to use them.

Good luck / Skip