I purchased this charger to maintain a deep cycle travel trailer battery. I tested the voltage on the battery and it was 12.6 volts before attaching the charger. One 24 hour period passed and the charger light was still on so I reviewed the instruction manual which suggested removing any drain on the battery. I disconnected the battery from the trailer and reattached the battery charger. Another 24 hours passed and the charger red light was still on. The voltage on the battery was then at 13. 67 volts but the charger was not in pulse trickle charge mode. I decided to return it to Amazon, which was easily done, and I bought the NOCO Genius 1100 trickle charger which recognized that the battery was fully charged and went into trickle charge mode. I would not recommend the Battery Tender for deep cycle batteries.