The Smart Troll II Probe Charger keeps the Probes fully charged between uses. The battery is sealed inside of the probe so to charge it you simply put the whole Probe in the charger between uses. 

The Probe batteries will last up to 8 hours in water below 50 degrees F and much longer in warmer water. If the battery in the Probe is completely discharged it may take up to 4 hours to fully charge (less time if only partially discharged).

You MUST remove the Probes from the charger once they are fully charged.