minivator 950 charging problem?

please please help, we bought my mum a second hand minivator 950 battery operated stairlift, the stairlift is not charging, bought a brand new charger and new batteries, still not charging , noticed there is only one copper strip on the rail, should there be two , also can see a spring/brush on the upper copper strip, we are charging batteries manually every 3 days. can anyone help, thank you