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I want to buy some NiMH batteries for a meter, the stocked NiMH that comes with the meter is 9V 300 mAh NiMH. Looking on eBay I found several NiMH batteries which appear to be 600 mAh, here is a link of the batteries : 9V Battery

Or this link (in case the other is broken):9V Battery

However, reading on Wikipedia and other sources I found that NiMH batteries have a maximum capacity of around 300 mAh, so my question is : Is a 9v NiMH battery with 600 mAh possible?, or are they just a Chinese gimmick that claims 600 mAh without actually delivering such capacity?

P.S. I cant use Li batteries on my meter.

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    \$\begingroup\$ TOFTT, buy some, test them, let us know how far they fall short. Maybe it's 600mAh for the two? \$\endgroup\$ – Neil_UK Jul 27 '17 at 16:56
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    \$\begingroup\$ Most of the well known brands offer 150-200mAh in this package. I don't think the Chinese developed new chemistry 4 times better :D \$\endgroup\$ – Todor Simeonov Jul 27 '17 at 16:56
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    \$\begingroup\$ I'd put as much trust in these as in the "10000 mAh" 18650s I just viewed on fleabay... Besides NiMH has high self-discharge, and a multimeter usually takes months to drain the battery, so it would be a weird choice... \$\endgroup\$ – bobflux Jul 27 '17 at 17:01
  • \$\begingroup\$ The multimeter im using is the Agilent/Keysight U1253a which has a rated 8hrs of battery life using a 300 mAh NiMH battery, I was hoping to extend it to 16 hrs using a 600 mAh battery. \$\endgroup\$ – S.s. Jul 27 '17 at 17:06
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    \$\begingroup\$ No. lygte-info.dk/review/batteries9V/… it's a scam! feedback.ebay.com/ws/… \$\endgroup\$ – Bruce Abbott Jul 27 '17 at 17:36
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I just bought a set of Lithium ion rechargable batteries. Here is the straight dope. Lithium Ion has a much greater energy density than NiMh. In addition, a 9v battery is made up of many cells. Since a NiMh chemestry is 1.2v, usually they have 7 little cells in there to make 8.4v. Since these cells are tiny, they do not hold that much energy. A Lithium Ion cell produces 3.7v and so they put 2 of these in a 9v battery package. It runs at 7.4v but that's ok for most things however it may always indicate that your battery is low. But since the 2 cells are much bigger, they can hold more total energy. The ones I have actually have a micro usb port in the bottom to charge so its sacrificing some power for convienence while still having more capacity than the NiMh. Its probably a good thing however because charging a Lithium Ion battery in a NiMh or NiCd charger will probably cause damage or explode.

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An AAA NiMH delivers a max of 800 mAH (irrespective of what it says on the label). So 600 mAH would be 3/4 times as big. 7 of those would be close to 9V. 3/4 of 7 is 5.25. So, is it possible to fit 5.25 AAA cells in a 9V space? I doubt it, especially considering that the 9V battery has an additional layer of packaging. I'd say, at most 500 mAH may be the absolute max possible, if one tries really hard. 300 mAH - 400 mAH is more realistic, especially if you want the low self discharge type.

As per comments below, an AAAA cell could potentially be 480 mAH max. 6 such alkaline cells typically make up an alkaline 9V. So for an NiMH 9V, if you have more than 6 cells in the same space, the mAH will almost definitely be less than 480 mAH.

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AAAA NiMH exist, and are 400 mAH. However, you need 7 of them for 8.4V (nominal). Or, you can make a 7.2V 400mA battery with 6x AAAA, that looks like a 9V battery (PP3 battery).

6x NiMH will typically be at 8V for most of it's life, at <100mA current draw. I use this often (6x AA NiMH). This is not as bad as it sounds. Remember that most manufacturers rate the alkaline cell mAH down to 0.9V. That means 5.3V for an alkaline PP3. 8V is way better than that.

Also, somewhat unrelated, but... Rechargeable cells are best charged singly. In a battery, if any cell is more damaged than the other, there exists a chance of polarity reversal during charging, which will destroy the pack. The chance of this happening, increases with every additional cell in the pack.

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  • \$\begingroup\$ 9v batteries sometime are made of 6 AAA cells so yeah they could. \$\endgroup\$ – Passerby Jan 6 '19 at 0:01
  • \$\begingroup\$ @Passerby You are confusing AAA with AAAA. Yes, there is such a beast! 9V batteries often have 6x (somewhat smaller) AAAA in them. However, I do not know of any AAAA NiMH cells. Also, AAAA cell occupies 0.6 times the volume of an AAA cell. This would make it 480 mAH max if it did exist. Also, we need 7 cells for NiMH, so mAH will decrease further. \$\endgroup\$ – Indraneel Jan 6 '19 at 1:29
  • \$\begingroup\$ Ah. I read that as 5.25 AAAA. \$\endgroup\$ – Passerby Jan 6 '19 at 3:45
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My solar garden lights came with Chinese 300mAh and 600mAh AAA Ni-MH cells. They both measure about 120mAh. Energizer 9V Ni-MH batteries are 175mAh but the Duracell website is not secure and is impossible to navigate.

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