The cell impedance is very important for many users. But here:
https://www.electro-tech-online.com/custompdfs/2010/08/powergenix-specs-aa-1.pdf
It seems pretty low. 3C (4.5A from the AA) is not an unacceptably high drop in voltage.
The exciting part is the charging cycle appears to be one where the cells could be paralleled to scale up to a larger batt, which can't reliably be done with NiMH. And the charge termination is straightforward like lithiums, not that transient dv/dt dip of NiMH which can be missed.
I wonder how the cycle life is? I didn't see a figure, and it's kinda beside the point because mfg-supplied figures and real-word figures are often two different things. And will they be damaged by deep discharge? NiMH can be taken down to 0V without damage. Lithium ion/li-po/lifepo4 will be damaged if you go below a certain voltage.
Note they can't be trickle charged like NiMH. The charge MUST be terminated.
The difficulty in scaling this up is that nickel is VERY expensive, and in limited supply. Like $60/lb IIRC. If you want much more for everyone to have an electric car, well, there isn't much more even if the price goes up. Lithium, however, well the brine pools it comes from now seem to have quite a bit, and if more is needed, it's a common element and there are plenty of other sources it might be possible to get it from.
Hi Oznog,
Some good questions.
I didnt think yet about parallel operation, but yes that is probably an option. I dont like paralleling the other battery types. Yes, the charge termination is quite simple really, which i also like very much.
I dont know how the cycle life is yet. We'll have to see i guess as i test them as time goes on. I also dont know if deep discharge hurts them, but i dont think so at this point except they may not charge on the charger as with their charger the thing looks for various fault conditions. All they say is (get this), "If they dont take a charge because the charger rejects them, try again in 24 hours". All i could think was, wow, that's nasty.
Well, they actually are to be trickle charged to get the full charge but only for 4 hours, not to exceed 48 hours. That's after the fast charge of 1C or something like that though, not a full trickle charge to full charge. The trickle charge for the AA is 75ma but again it is really only supposed to be for 4 hours and only AFTER a normal fast charge.
Yeah i guess we'll have to see how the pricing goes over time too.
So far i found out a few more things about these cells after some tests which i'll enumerate here...
1. The cells come depleted, and when i first tried to charge them they didnt take a charge but the next day they did.
2. The terminal voltage is not 1.6 really, it goes as high as 1.8v after a full charge. That's pretty high so i would want to be careful about what i used them in. I had seen on the web that some people blew their flash units out, but that was because they were heating up (supposedly) from the more rapid cycle times. Still, 1.8v is considerably higher than 1.6 when there are a number of cells in series. This gets a big "CAUTION" from me anyway.
3. The Watt Hour capacity is different than the Ampere Hour capacity, im sure most of us know already, but for these cells that means the capacity in Ah comes out to only 1500mAh. That's a bit low these days. To top it off, one cell tested in at only 1000mAh and i wrote to the manufacturer about this. It could be because the impedance goes down with more charge cycles (this was the first one) and makes the voltage stay higher so the capacity can be measured as higher, but i'll have to wait till i drain them a few more times to tell for sure.
4. I have read that the Sub-C size was being used in Europe for cordless power tools, but was unable to find a supplier.
Conclusions so far:
Because there seem to be pro's and con's for these cells, it's starting to look like the only time we would want to use them is when we have a device that absolutely needs higher voltage to work properly, and doesnt work well with regular NiMH. NiMH are tried and proven, and yes their terminal voltage is lower, so that seems to be the technology to stick with unless you really need the higher voltage.
Supposedly they handle the high current demands of cordless tools so the Sub C size is supposed to be good for them. This could be a big boom to the industry for this application but i still have to see it work to say if it is really good or not.