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Sunday, 23 March 2014

A simple guide to selecting rechargeable Ni-MH batteries and chargers and ways of using them to get optimum results

Rechargeable batteries are a very important commodity when you use heave drain devices like Cameras, huge toys,flashes etc.

Disclaimer : You take responsibility for whatever way you charge your batteries. This is just a piece of information, not a fact. Use your common sense. Your safety is the most important. Have a look at the caution information at the end.

The most popular AA or AAA size batteries are the NI-MH batteries. (Nickel - Metal hydride). They have good cycling times and recharge overnight.

What capacity of rechargeable batteries should I use? 
Battery capacities are denoted in mAh (milli Amp hours). The higher the capacity, the higher it will last before needing another recharge which means more usage time. The higher the capacity, the better.
Standard capacities to choose from, are anywhere from 1800 to 2800 mAh to have a pretty charge cycle.

How long can these batteries be charged and discharged?
Ni-MH batteries have a limited charge-discharge cycle (so does every other battery). It will be written on the battery wrapper somewhere.

What are the best applications for rechargeable batteries?
As stated earlier, they are best used for high drain devices. Low drain devices like TV remotes and alarm clocks are not fit for rechargeable batteries, because these batteries discharge themselves with less usage needing you to recharge again.

How long should these batteries be charged for the first time? / What type of charger should I use?
There are all kinds of chargers available to detect full charge and stop the battery from overcharging.
If your charger does not have such detecting ability, it is safe to charge the battery for the following duration:

Please note that this is only an example! Please refer to your charger manual for charging with it.

Duration of charge = (1.3 x Capacity of the battery/charge current of the battery) - 1 hour.
(I calculated the capacity and reduced the hours by 1 to prevent overcharge and overheating.)

For example, if you have a 2000 mAh battery and your charger's charge current is 200 mA.

Then, Duration of charge = (1.3 x 2000/200) - 1 = 13 -1 = 12 hours. Well, that's a rough estimate.

How long to charge them after the first charge (subsequent charges) ?
It depends upon your usage levels.

For example, camera flashes do not drain the battery completely. You will notice that the battery performs good in a torch after being notified from the camera flash as low battery after some usage.

In that case,  since that battery is not drained to the fullest, you can recharge it with the following approximate duration.

Duration of subsequent recharge (not fully drained) = Duration of first recharge (from previous formula) - 2 to 3 hours.

For example for the above 2000 mAh battery , duration of subsequent recharge = 12 -3 = 9 hours.


However, if you feel that the batter is drained to its core, either because it is left unused or the product has consumed the battery fully, please feel free to recharge it, the way you recharged it the first time.

Duration of subsequent recharge (fully drained) = Duration of first recharge (from previous formula).

I guess that helps.
The above said are only guide lines, your common sense over rides anything; always remember that.

Care / caution while charging/using/travelling....

Do not keep the batteries completely closed  in a sealed compartment during charging. In case of over charging, the batteries have tiny vents in the +ve side which release gases.

Do not over heat batteries above 35 Deg.C which may cause reduction in life.

Do not connect the positive and negative sides of the battery even by accident (by putting them in pockets). They tend to explode.

Do not overcharge your battery. The formula listed above is only a sample. It is better to have a small charge current charger as it gives more time to the battery to vent it out instead of bursting.

Do not drop these batteries. If you see visible damage in them, make sure you discard them. 

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