Use a VDC Electronics BatteryMINDER Plus. It was suggested I try using this charger vs. a Deltran Battery Tender and so far I've had no issue's. The Battery MINDER maintains, chargers and conditions the battery and has an auto-float control. My Deltran failed to keep my battery fully charged for some reason, so far the BatteryMINDER has kept it fully charged in top condition.
The BatteryMINDER got great reviews on WebbikeWorld and the cycle rags.
The BatteryMINDER got great reviews on WebbikeWorld and the cycle rags.