Cause:
i.) Over time the ability of NiMH and the now rare NiCad packs to hold and deliver a full charge, declines.
The result of this for example, is that a 2200 mAh. pack can easily become a 1100 mAh pack.
ii.) Memory effect (brought about by recharging a partly discharged battery pack) can lead to undercharged packs.
While battery packs with these problems may still work well, if model pilots are unaware of the deterioration in capacity, then they can be caught unawares and lose the RF link while in flight, leading to Failsafe activation and damaged aeroplanes.
Fix:
Measure and create the pack's discharge curve, periodically, (say once per year)
Example:
In the example above the data is taken directly from a digital charger at five minute intervals, and put into a simple spreadsheet.
In the above example from a full charge, this 1.0 Amp discharge curve of a 5 cell 2000 mAH NiMH transmitter pack shows performance to be reduced by one half.
Five cell NiMH packs have a nominal voltage of 5 * 1.2 = 6 volts. Here, after less than an hour's discharge at approx. 1 Amp, the pack is down to 4 volts under load. If all was well with the pack, we should be expecting two hours at 1 Amp .
There are two causes:
1.) Memory Effect.
This is rarely seen in modern NiMH packs but can occur.
2.) The pack is at the end of it's useful life and will not hold a full charge.
Before discarding the pack, check the real status by recharging and then performing another discharge test, (a charge/discharge cycle).
If the pack takes a full charge, and then delivers a full discharge, then memory effect has occurred and has been cleared by the charge/discharge cycle. This means the battery can continue to be used provided an eye is kept on things by periodic cycle charging.
If the pack will not take a full charge and has a significant shortfall, it should be replaced, especially if the nature of the function is critical, to supply power for the TX or Rx for example.
In the example below the same pack was recharged and found to accept a full charge. The pack was therefore discharged again, and this time delivered that charge fully. i.e. the pack is restored.
