How To Store Nimh Battery Packs

How Do You Store NiMH Battery Packs? Having invested in NiMH Battery technology, it makes sense to look after them. Not all NiMH Battery manufacturers give the same advice and instructions on this, so take some time to read what the top battery manufacturers have to say about storing their NiMH Battery Packs. Please see disclaimer at bottom of page.

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Storing VARTA NiMH Battery Packs

VARTA NiMH Batteries may be stored whilst at any state of charge and may be kept safely at the recommended temperatures of between -20 and +35 C. Relative humidity has a part to play also and this should be approximately 50%. For long term storage the NiMH Cells should be fully recharged once a year.

Storing Panasonic NiMH Battery Packs

In order to avoid accelerated battery self discharge during long periods of storage (leading to the deactivation of re-active materials), it is recommended that long term storage locations are kept between the temperature ranges between +10°C and +30°C. When re-charging for the first time after an extended period of storage, the de-activation of re-actants may lead to increased battery voltage and decreased battery capacity. To help restore these NiMH batteries to their original performance repeat several cycles of charging and discharging. Should battery storage for more than one year be required, charge at least once a year to prevent leakage and deterioration of performance due to self-discharging.
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Storing Sanyo NiMH Battery Packs

The recommended storage temperature range is between -20 C and +35 C. Additionally, the Twicell core can be stored indefinitely in either a charged or uncharged state. Recovery and recharge of Sanyo NiMH cells may take several cycles.

For batteries that are stored for a prolonged time whilst connected to a load, it is likely that electrolyte fluid will leak and the battery structure will start to deteriorate resulting in impaired quality after the storage period. During extended storage periods it is probable that battery deactivation may occur with the result that re-charging may be halted prematurely during recharging after storage. To remedy this, re-charging and discharging the battery several times should result in the battery capacity reaching pre-storage levels.

In general terms: a loss of voltage and capacity of Sanyo NiMH batteries will occur due to self-discharge during the storage period. The reasons for this self-discharge of Nickel-Metal Hydride batteries are as follows:

• The core of the NiMH cell contains a hydrogen atmosphere which is a at low pressure, this gradually reduces the active materials at the +ve electrode, resulting in a reduction of cell capacity. Accompanied by this, the -ve electrode which is thermo-dynamically unstable in its charged state gradually emits hydrogen gas, also reducing the cell capacity of the NiMH battery.
• The active materials contained at the +ve electrode whilst in its charged state self-decompose, causing the cell capacity to decrease. 
• Impurities within the NiMH cell, especially the nitric ions, are reduced at the -ve electrode and are attracted to the +ve electrode where they are oxidized. This also contributes to the resultant reduction of cell capacity.

The self-discharge characteristics of Nickel Metal Hydride batteries is also affected by storage temperature. If the NiMH battery is stored at high temperatures, the rate at which self-discharge occurs will be accelerated. Additionally, the longer the storage period, the more the cell capacity decreases. However, the capacity of Nickel Metal Hydride batteries lost by self-discharge can be effectively restored by fully recharging with the result that there are virtually no noticeable negative effects caused by battery storage. Either fully charged or discharged, Sanyo Nickel Metal Hydride ( NiMH ) batteries may be stored indefinitely and battery capacity is restored within two or three charge / discharge cycles.

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Disclaimer: Please note that whilst every effort is made to provide accurate information, these guidelines and  instructions for indicative and are subject to change by the Battery Manufacturers. We therefore always advise you to seek specific NiMH Battery Pack storage instructions directly from the manufacturer.)