I use a Battery Tender Junior on my starting battery during the winter while the boat is in the garage. It is not a battery charger. If the charge on the battery falls too low, it will not bring it up to charge. I have to use a charger then. But it does a nice job of maintaining the battery's charge while I store my boat for the winter in my garage. I just keep it hooked up to the battery. I have a Minnkota on board charger for my trolling batteries that I leave plugged in all winter. Just make sure your batteries don't go dry.