Invacare TDX SP Power Chair - Battery Level Indicator Problem

I bought an Invacare TDX SP Power Chair in May 2015. The battery level indicator on the joystick shows a full charge immediately after it's unplugged from the charger after about a half hour it drops three or four bars then will go up to almost full and continues to be sporadic all day. If I turn the chair off and back on sometimes it will show a full charge again but soon drops. It's dropped down to no bars and the screen will turn red and say charge batteries but then will go back up a couple bars. The batteries have been replaced and the charger is good but the problem continues. I never know if I'm getting a false reading or not so it's difficult to go to far not knowing if the chair is going to lose power. So far it hasn't lost power.

Has anyone else with an Invacare TDX SP experienced this problem? The vendor I purchased the chair from has been in contact with Invacare but can't seem to get a answer on the problem. Any feedback would be helpful.

Thanks

Invacare TDX SP Power Chair - Battery Level Indicator Problem