U.S. Battery

Frequently Asked Questions

There are numerous correct ways to charge the batteries. Typically, charge at C/10 amperes, (where C = the 20 hour capacity of the system express in Ampere Hours) until the battery voltage rises to 2.583 Volts per cell (i.e. 7.75 volts for a 6V battery). Hold this voltage constant for 2 to 4 hours, and stop charging. A similar method would be to charge at the following upper limits and terminate the charge when the time limit is reached:

  • Charge Current = C/10 Amperes
  • Charge Voltage = 2.583 Volts per Cell
  • Charge Time = 10 Hours Battery temperature adjustment: reduce the voltage by 0.028 Volts per Cell for every 10 degrees (F) above 80 degrees (F), increase by the same amount for temperatures below 80 degrees (F).

Download the full detailed charging instructions

2.17 Volts per Cell adjustment for the temperature as above.

Determine how many amperes your application needs from the battery and for how long. Multiply the two to obtain Ampere Hours required. Increase this by 20% for a safety cushion, and from our capacity charts, match a battery which will deliver this many AH for the required time, and voltage. Connecting batteries in parallel adds AH, and connecting in series adds the voltage. In either case the energy (WH) storage capability is increased by the amount of energy each additional battery provides.

Click here for the U.S. Battery calculator

Any claims of lasting longer are based on selective data, as a marketing gimmick (i.e. selecting the best of one and worst of the other) and is misleading. Battery life, like anything else, cannot be precisely pre-determined, any more than the life of your car or humans. The actual life out in the field, when operated under identical conditions, is the only valid criteria. One way to differentiate the life and performance is to look at the amount of materials, and the type of materials used in making the product. U.S. Battery Manufacturing Company uses more of the life and capacity giving active material than our competitors. Plus the unique grid alloy, and state-of-the-art processing technology, gives you the best possible life and performance.

  • If the batteries are not already fully charged, this can be an indication of sulfated batteries which may be causing a higher-than-normal internal resistance. Capacity of the bank will be reduced and can be confirmed by running a load test.
  • An increase in bulk charge voltage and/or absorption time may be necessary to de-sulfate the battery bank. Increase bulk/absorption charge voltage in 0.05 volt per cell increments or increase absorption time in 15 – 30 minute increments as necessary.
  • If the battery bank is heavily sulfated, an equalization may be necessary. Perform an equalization charge if specific gravity readings are <1.250 or vary by more than 0.015 volts between cells.
  • Sulfated batteries may heat up more than usual. Follow the guidelines for controlling maximum charging temperatures.
  • This is most commonly caused by loose connections resulting in a high resistance connection. This resistance has caused heat buildup and melted the terminal connection.
    • Loose connections
    • Over-tightened connections
    • Improperly sized cables (too small) or cable/terminal connections not properly made.
    • Corroded connections
    • Improper use of washers/lock washers.
    • Too many connections on the same terminal
    • Discharge rates higher than recommended
  • If at or near 50˚C (120˚F) shut off charge and allow batteries to cool to 32˚C (90˚F).
  • If a single battery or cell in a string is hot, this may indicate a cell failure or short. Verify specific gravity for all cells and take voltage readings from each battery. Perform a load test to identify any cell failures and verify proper cell operation.
  • Check for any loose terminal connections that may be causing excess heat.
  • This may be caused by multiple parallel strings of batteries in a bank, which often result in charge imbalance. U.S. Battery does not recommended that a system exceed 3 strings of batteries connected in parallel.
  • Charge voltage may be too low. Verify they meet U.S. Battery recommended charging parameters for Flooded batteries.
  • An increase in Absorption charge time may be necessary. Increase in 15 to 30 minute increments as necessary.
  • If specific gravity readings vary by >0.050 points then it is safe to assume the battery has a bad cell.
  • Charge Current = C/10 Amperes
  • Charge Voltage = 2.583 Volts per Cell
  • Charge Time = 10 Hours Battery temperature adjustment: reduce the voltage by 0.028 Volts per Cell for every 10 degrees (F) above 80 degrees (F), increase by the same amount for temperatures below 80 degrees (F).

Download the full detailed charging instructions

  • As batteries age, some bulging of the side and end walls caused by growth of internal components is normal.
  • Due to the weight of electrolyte, some case bulging is normal with new batteries.
  • Excessive bulging may be the result of operation at higher than recommended temperatures (>120ºF or 49ºC) or from prolonged undercharge causing excessive sulfation. This can cause permanent loss of capacity and shorten battery life.
  • Severe bulging may be an indication that the batteries have been frozen. Freezing can do permanent damage to the internal components in batteries and could result in an exploded battery. Batteries that are frozen or have been frozen should not be used.
  • 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.
  • Charging voltages may be too high and/or Absorption time should be decreased to prevent overcharge. Usage may have decreased, reducing depth of discharge (DOD and the time required to recharge, causing the batteries to overcharge.
  • Decrease bulk/absorption voltage in 0.05 volts per cell increments as necessary.
  • Decrease absorption time in 15 – 30 minute increments as necessary.
  • Charging voltages may be too low and/or Absorption time may need to be increased to prevent undercharging. Usage may have increased, resulting in increased depth of discharge (DOD) and sulfation.
  • Increase Bulk/Absorption/Boost Voltage in 0.05 volts per cell increments as necessary.
  • Increase Absorption Time in 15 – 30 minute increments as necessary.
  • This is called gassing and is a normal process when properly charging your batteries. As lead acid batteries recharge, the voltage increases to the point that electrolysis begins. Electrolysis is the separation of water molecules into its constituent parts, hydrogen and oxygen. The gasses travel through the electrolyte to the top of the battery cell where they vent to atmosphere. The movement of the gasses through the electrolyte gives the appearance of boiling. Gassing mixes the electrolyte achieving a homogenous acid solution. Proper electrolyte mixing is essential to the continued performance of your batteries.
  • In severe overcharge, excessive gassing and water loss will occur. This will shorten battery life.
    • Decrease bulk/absorption charge voltage in 0.05 volts per cell increments as necessary.
    • Decrease absorption time in 15 – 30 minute increments as necessary.
    • Gassing can cause leaking to occur if the cells were overfilled. This will result in permanent capacity loss.
  • Leaking is not normal and is typically due to overfilling the cells, but can also be caused by excessive overcharging. Both causes will result in permanent capacity loss if not rectified. Refer to the watering and charging sections for guidelines.

Metric Conversions

Date Code

SDS (Dry)

SDS (Wet)

Average House Capacity

Capacity Chart

Ampere Hour Capacity

Search