2 posts tagged “rechargeable batteries”

Since posting A Tale of Rechargeable Batteries, the PowerEx charger has earned its keep.  Not only does it restore NiMH batteries that were no longer taking an adequate charge from a regular 'quick charger', it also allow me to accurately determine the capacity of NiMH batteries so that they can be matched into sets such that one battery does not become 'the weak link'. 

The PowerEx charger also appears to be useful in diagnosing the 'charge lifetime' of batteries.  I used 6 AA NiMH batteries of matched capacity in a label printer that gets intermittent usage.  When the printer stopped working, I did a normal recharge cycle.  Since the 6 batteries were in series, they should all have discharged by the same amount.  However, the PowerEX reported varying recharge amounts from 500 mAh to 2000 mAh.  Given that all the batteries started with the same capacity, my suspicion is that some were 'self-discharging' at a rate higher than normal.  All NiMH batteries will lose their charge over time - quality issues during manufacturing or breakdown of the internal battery components can accelerate this process such that the batteries quickly discharge even if not used.

In this case, I may have matched the 6 batteries in terms of initial capacity, but clearly not in terms of their ability to hold a charge.  Of the 6 batteries, the PowerEx charger results suggested that four should either be relegated to recycling or only used in high-draw devices where self-charge is less of an issue.

I have been using rechargeable batteries for a number of years, starting with nickel-cadmium and converting to nickel-metal hydride.  Although definitely better than disposable batteries, I have never been able to get even close to the number of recharge cycles advertised before the batteries no longer would hold a useful charge.. 

I recently purchased a Maha PowerEx C9000 WizardOne charger, which can handle any combination of four NiMH or NiCD, in AA and AAA sizes.  Each slot can be independently programmed to do a charge, refresh/analyze, break-in, discharge or cycle operation.  The refresh/analyze operation does a charge/discharge/charge cycle to determine the actual battery capacity, an indicator of battery health.  The break-in cycle 'forms' new batteries using an extended charging cycle and can also reactivate batteries that have not been used for a long period.

To speed up the refresh/analyze process, I tried topping up my batteries using my normal quick charger.  In a few cases, I found that the PowerEX charger would be able to charge the supposedly charged battery considerably further, sometimes up to an additional 50% of rated capacity.  This suggests that my quick charger was prematurely terminating the charge.  I have also seen cases where repeated refresh/analyze cycles significantly improved the measured battery capacity, from 1700 mAh to 2500 mAh in one case, and from 300 mAh (effectively dead) to 1400 mAh in another. 

At a minimum, the PowerEx charger will allow me to track battery capacity and ensure that all batteries in a set are matched (if one battery in a set has lower capacity, it becomes the 'weakest link').  Initial results suggest the charger will also significantly increase the lifespan of the batteries.  The one downside is the size: at 11 x 17 x 4 cm (4.5" x 6.5" x 1.5") it is a bit larger for travelling.