Over the years I have had very poor luck with 6 volt trickle chargers used for battery winter storage. They would last for only one season or less or voltage output was erratic. About three years ago I purchased a Black & Decker, Model BM3B 6/12 volt "Battery Maintainer" from Baccus Global, 877-571-2391 and it has been just great. Maintains battery at full charge and goes into an automatic "maintain" mode. I think I paid less than $20. for it about three years ago.