Battery FAQ

1. Memory, True or False?

Answer is, false and true. There use to be a problem with memory in nickel cadmium batteries. It has now been virtually eliminated by the chemists at the battery manufacturing companies such as Sanyo, Varta, Panasonic etc…

There still exists an affect called voltage depression which is not as severe as the old memory problem but does reduce the output voltage of a cell during a full discharge if the cell has been subjected to numerous shallow discharges prior. The cell has the current available to deliver but can’t deliver it at the normal cell voltage of 1.2 Volts, and may only deliver it at 1.1 Volts. This would correspond to a 1.0 Volt output voltage reduction in a 12 Volt battery pack.

2. Why Nickel Batteries Fail and How The Renew Cycle Works?

When a nickel cadmium battery expires, it is usually because one of the cells in the pack is damaged. The lowest capacity cell in the pack is subjected to the deepest discharge cycles and possibility of polarity reversal. Since this lowest capacity cell endures the most punishment, the overall performance of the battery will depend upon this cell. If nothing is done to prevent damaging reversal conditions, this cell will prematurely end the battery’s life.

To maximize the life of a battery, it is important that the cells work in unison. This is achieved by maintaining an even level of charge between cells. The renew feature of our battery analyzers and chargers achieves this through four steps.

  • Step 1 – Standard Discharge. The battery is discharged to 0.9 Volts/Cell removing most of the available energy from the battery.
  • Step 2 – Deep Discharge. The battery is carefully discharged to 0.6 Volts/Cell. This removes the remaining energy from the strongest cells. The deep discharge is done slowly using short, high current pulses that prevent damage to the lower capacity cells. After fully discharging the strong capacity cells we have removed any voltage depression they might have acquired. This restores their maximum output voltage for future discharges. Voltage depression is caused by insufficient discharge.
  • Step 3 – Standard Charge. The battery is fast charged. Nickel type batteries respond best to fast charging. Fast chargers help remove crystalline formations caused by slow charging and insufficient discharging.
  • Step 4 – Slow Rate Overcharge. The battery is charged at a slow rate for 2-4 hours. This step balances the cells within the pack by continuing to charge the low capacity cells to their maximum, while the fully charged cells enter overcharge. The overcharge will not damage the fully charged cells as they will just warm up a bit to dissipate the overcharge energy as heat.

In summary, the cells within a pack are fully discharged to remove any voltage depression and then charged and balanced through overcharge. This will hopefully eliminate the chance of a cell from entering a condition of polarity reversal during future discharges, maximizing its life. For best results and care, nickel type batteries should be run through a renew cycle every 2-3 months.

3. The Lifespan and Storage of Batteries?

Lifespan

The life-span of rechargeable batteries is affected by many parameters. Some of which are within our control, being mainly proper charging. Chargers that overcharge cause excessive heating and internal gassing that can shorten battery life. Chargers that undercharge leave the battery susceptible to cell imbalance and sulfating. Proper discharging is important to minimize voltage depression and maximize the cyclic use of the battery. Operation in elevated temperature environments is stressful on rechargeable batteries and will result in shortened cyclic and calendar life spans.

Storage – For best results all batteries should be stored in a cool dry place

Lead acid batteries should be stored fully charged and free of moisture and dirt between the terminals to help prevent self discharge and sulfating.

Lithium-ion batteries should be stored charged, or partially discharged (25-50%), in a cool dry area.

Nickel Cadmium and Nickel Metal Hydride batteries can be stored fully charged or discharged at temperatures of between -20 and 30 degrees Celsius for almost an indefinite period of time without suffering any loss in capacity. For safety reasons it might be better to store them discharged, but be sure to completely disconnect them from there load so there is no prolonged current drain. Even a small load will eventually bring the output voltage to zero and cause the cells to leak electrolyte. After long periods of storage the battery may resist charging at first, but a good charger or analyzer should be able to bring them back up to full capacity within a few cycles with no trouble.

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