Just in case you’ve been a little negligent in battery maintenance over the winter and your batteries won’t charge try this…… Plug the boat in and turn the battery switch to “Both” to connect both banks if you have more than one. Then turn on a passive DC appliance such as the cabin lights and put a load on the system with the charger energized. Leave it for a couple of hours and this just might kick start the battery charger. Once the charger starts you can turn the lights off and let the battery charge as you normally would.
Since a dead battery has no internal resistance and offers little or no load on the charger, loading the system in this way might just be enough to get the charger going. Most chargers need to see a small load in order to initiate.
By the way if this doesn’t work you’re going shopping.