How to prime a nickel based cordless power tool battery?

28th February 2020

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	How to prime a nickel-based cordless power tool battery


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			Nickel-based cordless power tool batteries (NiCd and NiMH) often need to be ‘primed’ or ‘conditioned’ for use before they will perform at their stated capacity and voltage.

			Priming is necessary because often the battery has been in storage before you purchased it. The electrolyte settles at the bottom during storage and is no longer dispersed through the whole cell, limiting battery performance.

			NiCd batteries need regular priming. It is best to prime them after every 30 charge cycles. NiMH batteries do not need priming so often.

			Some chargers have a setting to prime batteries and the process will be done automatically. Below is a guide on priming a nickel-based battery if your charger does not have a conditioning, priming or ‘refresh’ setting.

			Step 1 – Charge battery slowly If possible, charge the battery on a trickle charge, preferably at about a rate of one tenth of the battery capacity. This means you are charging the battery very slowly. This can take up to 24 hours. Let the battery cool when it has fully charged. Many chargers won’t have a trickle charge option, in which case charge the battery on its normal charge programme but leave it in the charger for 24 hours.

			Step 2 – Check voltage When the battery is fully charged, check the voltage using a voltmeter. It will probably be lower than the voltage it should be. When you repeat the charge cycle in Step 5, the voltage of the fully charged battery will increase each time until it reaches the voltage stated in the product description.

			Step 3 – Discharge the battery The simplest way to discharge a battery is to use it in a cordless power tool as you normally would until there is a decrease in performance of the tool. Stop using the tool and hold the trigger down to let the motor run, discharging the battery further.

			Step 4 – Check voltage again Using the voltmeter, check the voltage of the battery at intervals once the power tool has shown a decrease in performance. Keep discharging the battery in the power tool until the voltage decreases to about 0.9V.

			Step 5 – Repeat the cycle Repeat steps 1 to 4 a few more times. The slow charge will balance the cells, redistribute the electrolyte and break up any problematic crystals that have formed. Crystals forming on the electrodes prevent the battery charging fully, this is called the ‘memory effect’ because it has ‘forgotten’ how full it should be.

			Even after priming, a nickel-based battery may not perform at its best until it has completed 50 or more charge cycles.