I'm needind ti re-stock my ball machine. I used pressureless balls for around 18-20 months, and they still bounce fine. The felt has started to come off on them is all. Am I better off getting more pressureless balls, or buy new pressured balls and get one of the ball "chargers" that claim to retain the bounce in pressured balls? any experience on how long normal balls remain "like new" using the chargers?