Hi
As far as the NI-MH Batts are concerned this is the manufactures advice.
NiMH (Nickel Metal Hydride) Battery Storage
Duracell NiMH Battery Storage
Ni-MH batteries can give years of safe and reliable service if they are used in accordance with recommended procedures and are not abused. Batteries should be kept clean and dry both during use and storage. They can be stored for many months in a charged or discharged state without any detrimental effects as long as they are not exposed to extreme temperatures for any long period of time. After periods during which the battery has not been used, the battery should be charged before being placed in service. Extended overcharging or overheating of the battery should always be avoided.
Varta NiMH: Battery storage in any state of charge is possible. Storage temperatures between -20 and +35 are recommended, relative humidity approximately 50%. In case of long term storage cells must be recharged once a year.
Sanyo NiMH: Under the recommended storage conditions (-20 C to +35 C) the Twicel can be stored indefinitely in either a charged or uncharged state. Recovery may take several cycles. If a battery is stored for a prolonged time connected to a load, electrolyte fluid will leak, the battery will begin to deteriorate, and capacity will be impaired after storage. During long time storage battery deactivation may tend to occur, and for this reason charging may stop early during recharging after storage. This problem can be solved by charging and discharging the battery several times.
Sanyo NiMh Battery Storage: Generally speaking, a loss of voltage and capacity of batteries due to self-discharge during storage is unavoidable. The factors inducing this self-discharge of Nickel-Metal Hydride batteries is listed below:
The inside of the cell is a hydrogen atmosphere at low pressure, which gradually reduces the active materials at the positive electrode, resulting in a drop of cell capacity. Accompanied by this, the negative electrode which is thermodynamically unstable in its charged state gradually gives off hydrogen gas, thus reducing cell capacity.
The active materials at the positive electrode in its charged state self-decompose, causing the cell capacity to decrease.
Impurities within the cell, especially nitric ions, are reduced at the negative electrode and diffuse to the positive electrode where they are oxidized. This results in a lowered cell capacity.
Lionel