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I found these two batteries in a drawer while looking for batteries for my wireless mouse. I was surprised to see that they are 4500 mAh, which is much higher than any AA battery I could find on the Internet.

I don't have a way to measure the capacity, but I have a 180mA charger that I used to charge them for 25 hours (25*180 = 4500, half of 9000). Sure enough, when I put them in my wireless mouse, my computer showed that they're about 50% charged.

How is this possible? Do they mean 4500 for both batteries? Is my measuring strategy flawed? What can I use to measure their capacity accurately?

4500mAh AA batteries?!

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  • \$\begingroup\$ A Li-ion 18650 has a capacity of about 2600mAh. There is no way in hell that a NiMH 14500 is going to have that high a capacity unless they're fudging the test very strongly. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 6 '14 at 16:21
  • \$\begingroup\$ Don't try to compare Li-Ion with 3.7V to 1.2V NiMh. NiMH cells with 3000 mAh capacity can be bought from credible sources. \$\endgroup\$ – Turbo J Dec 6 '14 at 16:47
  • \$\begingroup\$ @TurboJ: Sure, but 4500? Nuh-uh. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 6 '14 at 16:54
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Let's see- unknown brand name, claims of storage capacity beyond that of any remotely trustworthy manufacturer, found in a drawer so likely not engineering samples liberated from a top-secret skunkworks, and inability to spell the word "battery" on the label (BRTTERY?).

The whole thing screams arbitrarily labeled Asian-made product of the most dubious of origins. If you're lucky they'll function and have 2000mAh capacity for a few hundred charges.

If your computer thinks there is an alkaline AA cell in there it will report about half capacity since the NiMH cells have a lower voltage (1.2V vs 1.55V) when fully charged and a flatter discharge curve.

You could test the battery roughly by fully charging it and discharging it with a resistor but you'd have to monitor it to ensure the cell voltage did not drop below about 1V or the battery could be damaged. Make a measurement every 30 min or whatever and plot the result.

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