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#### gjpollitt

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I have a AA 1.2v 1800mah battery and wanted to test if it was good or not what would be the best value resistor to load it with?

thanks for any help

gjpollitt said:
I have a AA 1.2v 1800mah battery and wanted to test if it was good or not what would be the best value resistor to load it with?

thanks for any help

Generally testing at 10% of it's rating is about right.

so what would be a good value to load the battery with? to get a good idea of if requires recharging or not?

From your specs it appears you have a NiCad battery. These have a very flat discharge curve, IOW, the voltage changes very little until the battery is almost empty.
So, testing it with a resistor load to find its charge would not be very useful.
Resistor load testing is more practical with non rechageable batteries.

Many years ago I plotted discharge graphs for various AA batteries, you can see them here .

gjpollitt said:
so what would be a good value to load the battery with? to get a good idea of if requires recharging or not?

As was already stated, a resistive test is not the best way to test your rechargeable cell. However, just in case there is anyone lurking who wants to know the answer to the resistive load question, here it is...

Assuming, as recommended above, that you want a load current equivalent to about 10% of the rated capacity of the cell, we would be looking for R in the equation R=E/I, where E is the (rated) cell voltage of 1.5V and I is the desired load current of 0.180A (180mA, or 10% of 1800mA).

So... R = 1.5/.180 = 8.333 ohms.

The closest standard value to this would be 8.2 ohms, and it would be advisable to use at least a 1/2W resistor for this.

I'd just like to confirm that Chris is correct with the 1/2 watt resistor. The calculated watts, given the values of 1.50 volts and .18A = .27 watts, which would either overload or slowly destroy a 1/4 watt resistor.

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