Hello! I'd like to find out, how do you store rechargeable batteries if you don't use them for a long period(month or more). As I know, they must have 10%-15% of power to store safely. I'm wondering, how to know their remaining charge and how to discharge them to this 10-15% (my spare battery after photo session if I haven't use it)
Thanks to all your ideas!!!

This is what I found:
It really depends on the type of battery in question, NIMH should be stored at full charge, and charged every month during storage. Nicad on the other hand can be stored fully discharged. Lithium Ion should be stored with a partial aprox. 50% but never allowed to discharge completely. One of the links I checked out is below:
http://www.batteryuniversity.com/index.htm

PETE KOSSARAS wrote:
This is what I found:
It really depends on the type of battery in question, NIMH should be stored at full charge, and charged every month during storage. Nicad on the other hand can be stored fully discharged. Lithium Ion should be stored with a partial aprox. 50% but never allowed to discharge completely. One of the links I checked out is below:
http://www.batteryuniversity.com/index.htm
!!!!!!Thaks a lot!!! That is, I want to know!!!!

Here's what I've found. You have high output batteries that are great for fast recharge rates (I'm talking about the time they take to be ready to fire the flash again not the time they take to recharge) and power output for flash. I find these to be preferable by far for flash work but they lose most of their charge when stored in a case within about a month. If however I keep them in a flash they hold a lot more of their charge for a lot longer. Those that I store outside the flash I recharge every month and before I go out to a shoot with them. I use the Maha Powerex 2700 NiMH.

The other type of battery is a slow loss battery. These provide much slower recharge rates for the flash but they hold their charge to say 85% for up to a year. I keep these on hand in case I haven't tended to my high output batteries and so they don't have a full charge. Here I use the Sanyo enloop NiMH.

Lithium-Ion batteries used for cameras and laptop computers hold their charges in storage well and don't have a memory problem. The charging is regulated by a microprocessor built into the battery and defective batteries have been known to overheat and cause fires. There was a big recall of laptop batteries made by Sony a few years ago.

NiMH batteries lose about 1% of their charge per day in storage. They need several charge / use cycles before reaching peak performance, which declines over time with use. Sanyo and MAHA are two of the better brands.

The newer Sanyo Eneloop batteries have lower capacity than NiHM (2000 mAh vs 2700 mAh) but hold their charge better in storage than traditional NiHM. They are sold charged and when fully charged will have 70% remaining after 6 months of storage.

Performance of NiMH and Enloop over the long haul is improved by using a microprocessor controlled charger which charges and monitor each cell separately and keeps the temperature of the battery low while charging. I used MAHA Powerex NiMH with a MAHA charger for several years for my flash batteries, but as they have reached the end of their useful life I've switched to Eneloops. It is best to use batteries in marked sets and replace the set when one cell starts to decline in performance.

Chuck

So, to sum up. We mostly use Li-Ion bat. for cameras and NiMH for flash.
To store back-up batteries for a long period we should stick to this rules:
1.Li-Ion bat we store at at 40% state-of-charge
2.NiMH at full charge.