I think I need a new charger?

The battery charger I currently have is a Imax b6 and it can't seem to charge any of my batteries to a full 16.8 volts. Even on balance charging mode it doesn't really balance the cells and one pack the cell voltage difference is as much as .5 volts off. Has anyone else run into something like this? I bought new batteries because I thought it was because they were 4 months old but even the new tattu 4s 45c 1050mah packs are only getting charged up to 16.7 volts with different voltages in each cell. The charger used to get all cells to 16.8 so I am thoroughly confused