Recently our daughter took our Stingray out and after getting it in the water found that the battery wasn't fully charged. They were about to haul it out (afraid that the alternator wasn't working) when a Good Samaritan pulled out a charger and charged it for them. It was not hooked up to electricity. This charger evidently stored power for use in situations where there was no electricity available. Does anyone know what this charger is called and where we can get one? We want to be able to charge a 12 volt marine battery in an emergency.