Capacity loss may be due to: Sulfation of the cells. Equalize batteries until all cells have a specific gravity >1.265. Overheating the batteries. Verify that temperature sensors are properly mounted and verify cell temperatures remain below 50°C (120°F) during charging. Over-discharging the battery bank. Capacity of the battery bank may no longer support an increase in load. Aging batteries. Towards end of life, batteries will slowly drop in capacity until only 50% of the capacity is usable. At this point U.S. Battery recommends battery replacement. Consistent undercharging. Verify that your batteries are receiving a full charge using specific gravity readings.