U.S. Battery Manufacturing Company, Inc. recommends the use of ‘opportunity charging’ or charging batteries and battery packs at every opportunity while in storage or service. Following this recommendation will assure that batteries are always at the highest possible State of Charge (SOC) to maximize performance and range and to minimize the battery’s Depth of Discharge (DOD) to optimize performance and life.

The charging process is intended to fulfill several objectives. First, the charging process should replace the capacity (in amp-hours) removed from the battery during previous discharges. Second, the charging process should return additional capacity (in amp-hours) to offset the thermodynamic inefficiencies inherent in the charging process. This additional capacity can be measured as a charge factor calculated by: charge Ah in / discharge Ah out. The charge factor varies with temperature, condition and age of the battery but is usually in the range of 105 – 150%. Third, the charging process should charge the battery at a voltage and/or charge rate at the end of charge that will result in controlled gassing of the electrolyte. This gassing is required to mix the electrolyte to prevent stratification. Without proper mixing of the electrolyte, the heavier acid generated during charging can sink to the bottom of the cell and will adversely affect performance and life of the battery. Finally, the charging process should result in a fully charged battery with electrolyte specific gravity that is constant over several end-of-charge readings, consistent between and among the cells of the battery pack, and within the proper range for the battery type per U.S. Battery’s specifications.

U.S. Battery is active in the development of new charging methods and regularly tests and evaluates new charger technologies. As part of U.S. Battery’s charging recommendations, charging methods are categorized into three basic methodologies based on the number of charge stages used in the charging process. It should be noted that the basic charge stages should result in a fully charged battery at the end of the final charge stage. Using this criterion; float charging, maintenance charging, and equalization charging are not considered to be one of the basic charge stages. These basic charge stage methodolgies can be defined as follows:

  1. Three-Stage Charging – Charging using bulk charge, absorption charge, and finish charge (usually constant current – constant voltage – constant current).
  2. Two-Stage Charging – Charging using bulk charge and absorption charge only (usually constant current – constant voltage).
  3. Single-Stage (Ferroresonant) Charging – Charging using a single-stage charge with tapering current and voltage.

U.S. Battery’s charging recommendations for deep cycle flooded lead-acid (FLA) and sealed absorptive glass mat (AGM) batteries are attached. Note that the charging parameters recommended for each of these depend on both the battery type and charger type. These charging parameters are often controlled by specific charge algorithms that can be selected or programmed by the user. Users should consult the charger manufacturer and/or U.S. Battery for proper selection or programming of algorithm controlled chargers. U.S. Battery prefers the use of Three-Stage Charging with dV/dt charge termination to minimize the charge time required for full charge and to reduce the risk of abusive undercharging or overcharging of batteries and battery packs.

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