Anyone use rechargeable Nickel Zinc batteries yet?

[watdahel]

I just found out that Amazon sells these new rechargeable AA Nickel Zinc batteries that provide higher voltages than your usual Nimh batteries. Supposedly they come in handy when your camera stops working with Nimh because due to its higher voltage the camera can keep on working longer. I am so tempted to get some but it's $25 for the batteries and charger.

 

[Zenmervolt]

It's not voltage that determines a battery's time to discharge, it's the amp-hour capacity (for small batteries this is typically rated in milliamp-hours). That's why 2500 mAh batteries last longer than 1800 mAh batteries even though both are 1.2 volt cells (assuming AA size NiMH).

Some older electronics are sensitive to the fact that NiMH batteries are 1.2 volt rather than 1.5 volt like alkalines, but the majority of modern devices have voltage regulators that account for variances in a battery's output voltage.

 

[pm]

Some of their selling points are a little deceptive - for example, as Zenmervolt said, PowerGenix quotes mWh (milli-watt-hours) instead of the more traditional mAh (milli-amp-hours).

To quote from one of the comments at Amazon:
- Energy in eneloop AA cell: 1.25V * 2000mAh = 2500mWh
- Energy in PowerGenix AA cell: 1.65V * 1500mAh = 2475mWh

So a cheaper and more compatible Sanyo Eneloop AA NiMH cell has about the same about of energy as a PowerGenix NiZn cell. The voltage is higher but the current capacity is much lower and so the result is more or less the same amount of usable energy.

The reviews at Engadget and other sites are glowing when it comes to very high discharge applications (ie. a hotshoe flash for an SLR camera), but for replacing your batteries in things like wireless mice and TV remotes where rechargeables can save a lot of money, they are worse than Sanyo Eneloop NiMH cells. The problem is the high self-discharge rate. The quoted rate from Powergenix is ~1% per day, so you'll have ~70% capacity left at the end of a month of sitting around, the quoted rate from Sanyo for Eneloops is ~0.04% per day. So at the end of a month, you'd have 99% capacity left.

I think the Powergenix cells are great for cameras - particularly high drain rate camers (like the ones from HP) - and for large flash units for cameras. But for things like flashlights and TV remotes and toys, the self-discharge of the Powergenix NiZN cells is too high and you'd be taking them out all the time to recharge them.

 

[corkyg]

The technology is not new, but has been advanced recently, and it has some advantages, especially for small devices.

http://en.wikipedia.org/wiki/Nickel-zinc_battery

 

[watdahel]

From my experience Nimh degrades to the point that it won't even power up a digicam due to voltage drop below a certain threshold even though there is still juice left. The NiZn battery perhaps has an advantage by having a higher starting voltage and can keep the camera running beyond where a Nimh would've been considered depleted by the camera.

Also, I have a Cree Q3 LED flashlight that uses a single AA battery. The Cree Q3 LED typically runs at 3.7 volts, I believe and so the flashlight employs a voltage booster to be able to run on a single AA battery. There is a noticeable difference in brightness between using a freshly charged Nimh and a fresh primary battery. The primaries are brighter. Based on that observation I would think a NiZn battery with its even higher voltage could be beneficial.

 

[Zenmervolt]

From my experience Nimh degrades to the point that it won't even power up a digicam due to voltage drop below a certain threshold even though there is still juice left. The NiZn battery perhaps has an advantage by having a higher starting voltage and can keep the camera running beyond where a Nimh would've been considered depleted by the camera.

Also, I have a Cree Q3 LED flashlight that uses a single AA battery. The Cree Q3 LED typically runs at 3.7 volts, I believe and so the flashlight employs a voltage booster to be able to run on a single AA battery. There is a noticeable difference in brightness between using a freshly charged Nimh and a fresh primary battery. The primaries are brighter. Based on that observation I would think a NiZn battery with its even higher voltage could be beneficial.

Given most people's typical use patterns for flashlights, a NiZn battery's 1%/day self-discharge rate would make it a ridiculously poor choice in a flashlight.

A look at the discharge curves for alkalines vs NiMH batteries shows quite clearly that NiMH cells don't drop significantly in voltage until they are extremely close to a fully-depleted state (see the last graph here), especially at very high discharge rates. Even at lower discharge rates, the point at which NiMH cells drop below their rated value and the point at which Alkaline cells drop below that same represents about the same relative amount of discharge (alkaline AA batteries and the 2000mAH NiMH batteries both drop below 1.2 volts at the 1.6 amp-hour mark), which would mean that both are roughly equal in actual staying power.

It does look as though the NiZn batteries would be well-suited to high-drain devices like camera flashes, but, frankly, I don't have any issues with my flash's cycle time with the 2500mAH NiMH batteries I use now and with 2500mAH at 1.25 volts, the NiMH batteries trounce the NiZn in mWH as well, with 3125mWH compared to 2475mWH.

I'm not against NiZn; it's a good technology. At the moment though I think it's something of a solution to a problem that doesn't exist.

ZV