The rate of battery recovery by applying controlled discharge/charge cycles varies with chemistry type, cycle count (mileage), maintenance practices and age of the battery. The best results are achieved with the NiCd. Typically 60% to 70% of discarded NiCd batteries can be restored to full service when using the exercise and recondition methods of a Cadex battery analyzer or equivalent.
Not all batteries respond equally well to exercise and recondition. An older battery may show low and inconsistent capacity readings after servicing, another may even get worse with each cycle applied. Such conditions indicate instabilities in the battery and these packs should be replaced. An analogy can be made to a very old man for whom exercise is harmful.
There are older NiCd batteries, however, that recover to near original capacity when serviced. Caution should be applied when "rehiring" these old-timers because they may exhibit high self-discharge . If in doubt, a self-discharge test should be carried out.
The recovery rate of the NiMH is estimated at 40%. The lower yield is, in part, due to the NiMH’s reduced cycle count as compared to the NiCd. NTT, a long time user of NiMH batteries in Japan, has reported a good recovery ratio of NiMH batteries when using Cadex’s exercise and recondition methods.
The recovery rate for SLA is a low 15%. Unlike nickel based batteries, the restoration of the SLA is not based on breaking down crystalline formation, but rather on reactivating the chemical process. The reasons for low capacity readings include prolonged storage at low terminal voltage and poor charging methods.
Capacity loss of Li-ion batteries consist of recoverable and non-recoverable losses. Optimum ways to restore the recoverable losses will likely be developed in the near future. At the present time, no reliable method to restore these batteries has been established.
When servicing Li-ion batteries with a battery analyzer, the purpose of maintenance is not so much in restoring batteries affected by memory (the Li-ion batteries do not exhibit memory), but to check the performance of new batteries, to assure proper capacity levels before the warranty expires, and to weed out the deadwood once the capacity has fallen below an acceptable target level. Battery maintenance also helps identify poorly performing chargers.
A question commonly asked is "will a restored battery be like a new one?" An analogy can be made with replacing a defective part on a machine. Only the replaced part is new; the rest of the machine remains in the same condition. If a battery contains a separator that was damaged by excess heat or marred by uncontrolled crystalline formation, for example, that part of the battery will not improve. The breaking down of the crystalline formation on a NiCd or NiMH can be considered a full restoration. However, the crystalline formation will re-occur with time if the battery is denied the required maintenance.