Care & Maintenance of Deep Cycle Batteries

  • New batteries should be given a full charge before use
  • New deep cycle batteries need to be cycled several times before reaching full capacity (50-125 cycles, depending on type). Capacity will be limited during this period
  • Battery cables should be intact, and the connectors kept tight at all times. Always use insulated tools to avoid shorting battery terminals. Regular inspection is recommended
  • Vent caps should be correctly installed and tight during operation and battery charging
  • Batteries should be kept clean and free of dirt and corrosion at all times
  • Batteries should always be watered after charging unless plates are exposed before charging. If exposed, plates should be covered by approximately 3mm of electrolyte (add distilled water only). Check electrolyte level after charge. The electrolyte level should be kept 6mm below the bottom of the fill well in the cell cover
  • Water used to replenish batteries should be distilled or treated not to exceed 200 T.D.S (total dissolved solids… parts per million). Particular care should be taken to avoid metallic contamination (iron)
  • For best battery life, batteries should not be discharged below 80% of their rated capacity. Proper battery sizing will help avoid excessive discharge
  • Battery chargers should be matched to fully charge batteries in an eight hour period. Defective and unmatched chargers will damage batteries or severely reduce their performance
  • Avoid charging at temperatures above 48°C or ambient, whichever is higher
  • As batteries age, their maintenance requirements change. This means longer charging time and/or higher finish rate (higher amperage at the end of the charge). Usually older batteries need to be watered more often as their capacity decreases.
  • Deep cycle batteries need to be equalised periodically. Equalising is an extended, low current charge performed after the normal charge cycle. This extra charge helps keep all cells in balance. Actively used batteries should be equalised once per month. Manually timed chargers should have the charge time extended approximately 3 hours. Automatically controlled chargers should be unplugged and reconnected after completing a charge
  • In situations where multiple batteries are connected in series, parallel or series/parallel, replacement battery(s) should be of the same size, age and usage level as the existing batteries. Do not put a new battery into a pack which has 50 or more cycles. Either replace with all new or use a good used battery(s)
  • Periodic battery testing is an important preventative maintenance procedure. Hydrometer readings of each cell (fully charged) gives an indication of balance and true charge level. Imbalance could mean the need for equalising; often a sign of improper charging or a bad cell. Voltage checks (open circuit, charged and discharged) can locate a bad battery or weak battery. Load testing will pick out a bad battery when other methods fail. A weak battery will cause premature failure of companion batteries
  • Always use a matched charger and battery pack system. Unmatched chargers will cause potential problems
  • Lead acid batteries should be brought up to full charge at the earliest opportunity. Avoid continuously operating batteries in a partially charged condition. This will shorten their life and reduce their capacity.
  • Extreme temperatures can substantially affect battery performance and charging. Cold reduces battery capacity and retards charging. Heat increases water usage and can result in overcharging. Very high temperatures can cause “thermal run-away” which may lead to an explosion or fire. If extreme temperature is an unavoidable part of an application, consult a battery/charger specialist about ways to deal with the problem
  • Inactivity can be extremely harmful to all lead acid batteries. If seasonal use is anticipated, we recommend the following:
    • Completely charge the battery before storing
    • Remove all electrical connections from the battery, including series/parallel connectors
    • Store the battery in as cool a place as possible. However, do not store in a location which will consistently be below 0°C. Batteries will discharge when stored, the lower the temperature the lower the self-discharge
    • When not in use, boost every two months

Additional Points Worth Considering

As mentioned previously, charging of lead acid batteries to fully charged generally takes between 6-8 hours but 80% to 90% of charge can be returned in much shorter times. In practice house batteries rarely become fully charged while in use. If the batteries are not periodically taken to a fully charged state (say every two to three months) a portion of the capacity is permanently lost. Correct maintenance practices must be followed.

The higher the battery capacity of a battery the greater the ability of the battery to absorb power. This is another reason why correct battery sizing is critical.

Care should be taken when working around batteries, particularly when they are on charge or have recently been charged. Batteries emit explosive gases which if ignited can cause serious injury, particularly to the eyes. Safety glasses should be worn at all times when working on or around batteries.

When doing the design for a new installation, or the addition of accessories, it is advisable to take into account possible additions of electrical load. For example if you are considering installing a microwave oven at some stage in the future, consideration to the increased load should be made. This may be in the form of allowing for an additional battery bank to be added (say in parallel to the existing one). The addition of an accessory which significantly increases the load on the batteries and charging may stress the system to such an extent that problems will arise.

Charging voltages are critical. Small differences in charging voltages (as low as 0.4V) can have significant effects. This is easily understood when remembering that the voltage rise, which causes charging current to flow, is very low. A 50% discharged battery has a terminal voltage of around 12.2V. A charging voltage of 14.0V represents a 1.8V rise. A charging voltage of 14.6V (the recommended for flooded deep cycle batteries) provides a rise of 2.4V. This is 33% higher than that which is provided by the lower charging voltage. Charging current is proportionally higher and charging time using the higher charging voltage is significantly reduced.

The 14.6V charge rate setting also induces gassing within the cells which mixes the electrolyte. Stratification of the electrolyte occurs when charging and discharging of the battery takes place. Discharge produces water which is lighter and floats to the top. Charging produces acid which is heavier and tends to sink to the bottom. Most common cause of poor battery performance is insufficient charging voltages. Lower recharge voltages often result in shortened battery life.