The recharger will help you give new career energy for your players.
Add a player to a recharger and they will after a few days get extra energy to play more matches during their career.
Tip! Keep your best 3-6 players. They can be used on and off for ever if you use the recharger smart. So no need to dismantle your absolute best players once they run out of energy.
This is made so you can keep your club legends for ever!
Note that players who has been overclocked are a little harder to recharge. It does not mean it is a bad idea to overclock, but it is something to consider before overclocking your club legends.