Nauticraft recommends using an AGM sealed marine grade battery in the electric boat models.  The AGM has advantages over other types of batteries being it is more stable under charge than a Gel Cell, it is less likely to lose it’s charge when setting unused as a flooded wet cell does and it is maintenance free.  Even so, it is possible to have some charging difficulties with the AGM battery.  If your battery has been sitting for a few months or if it was depleted to less than 25% on the LED  Meter it may be helpful to put it on a trickle charger for 24 hours.  When you connect the higher amperage charger to a less than charged battery, the charger is unable to read any level at all coming from the battery, and it won’t process through the cycles.  If you’ve used a trickle charger and give it a good boost, the 6 amp charger will recognize there is a battery connected to it and do what it is designed to do!