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331 of 338 found the following review helpful:
 Showdown: PowerGenix NiZn vs. SANYO eneloop NiMH Oct 29, 2009
By NLee the Engineer
The product description of PowerGenix Nickel-Zinc Rechargeable AA cell promises many advantages over other rechargeable batteries: higher voltage, higher energy density, lighter weight, longer cycle life, and so on. But how does it stack up against the current gold-standard of low-self-discharge NiMH cell, the Sanyo Eneloop? Let's examine the following aspects:
[Operating Voltage]
The NiZn cell has a nominal voltage of 1.65V, which is 30% higher than that of a NiMH cell (1.25V nominal). When freshly charged, its terminal voltage is even higher at 1.85V!
[Power Density]
Since 'Power' is defined as 'Voltage * Current', most people may assume that "30% higher Voltage" translates to "30% higher Power". But it depends on the application:
- Most electronic gadgets (digital camera, MP3 player, etc) contain internal DC/DC regulators which operate in constant-power mode. If the battery voltage is higher, then input current will drop to maintain the same output power. That's why higher voltage alone does not make your digital camera shoot any faster.
(One exception is photo flash unit, which operates in constant-current mode. So in this case, 30% higher voltage does translate to 30% higher power and shorter cycle time)
- For an unregulated appliance such as a flashlight or power tool, its current increases with voltage (although not linearly). A typical 2-AA flashlight bulb is rated for 2.3V * 0.5A = 1.15W. When you apply 3.6V to it, the current may increase to 0.65A, so the power consumption is now 3.6V * 0.65A = 2.3W. Twice the power means twice the heat. That's why the bulb may burn out in seconds.
[Energy Density]
The PowerGenix AA cells are marketed as "2500 milli-WATT-hour" (energy capacity). Most people may confuse this with "2500 milli-Ampere-hour" (charge capacity). But the data sheet for NiZn AA cell shows that its current capacity is only 1500mAh (this is verified by my own testing). It turns out that an 1500mAh NiZn cell actually contains the same amount of energy as a 2000mAh SANYO eneloop AA cell:
- Energy in eneloop AA cell: 1.25V * 2000mAh = 2500mWh
- Energy in PowerGenix AA cell: 1.65V * 1500mAh = 2475mWh
[Weight]
The weight of each NiZn AA cell (25g) is essentially the same as that for eneloop AA cell (27g). For certain applications, it is possible to use three NiZn cells (3*1.65=5V) to replace four NiMH cells (4*1.25V=5V). Doing so reduces battery weight by 25%, but it also shortens run time by 25%.
[Cycle Life]
Technical data found on PowerGenix web site says NiZn cells are rated for 200 cycles (at 100% deep-discharge). This is much shorter than the 1000 cycles cited for eneloop cells.
I have tested a set of 4 PowerGenix AA cells. After subjecting them through 12-16 deep discharge cycles, the average charge capacity already dropped 5% from original value. In comparison, I have a set of 4 eneloop AAA cells that have went through about 100 cycles in the past 2.5 years, and they still exhibit over 95% of original capacity.
[Self-Discharge Rate]
In my long-term storage test after two months, a set of four NiZn cells retained 74% original charge capacity on average. This translates to about 13% loss per month, which is much better than that of ordinary high-capacity NiMH batteries (with capacity > 2500mAh). But it cannot compare to low-self-discharge NiMH cells.
Previously, I have conducted storage test for several brands of LSD cells, including Sanyo eneloop, Rayovac Hybrid, and Kodak Pre-Charged. All those cells can retain 85-90% of original capacity after FIVE months in storage.
[Recharging Time]
The PowerGenix NiZn cells must be recharged using a specially designed PowerGenix NiZn Charger. The charger is called '1-hour', but it actually takes 2.5 hours to fully recharge a set of four 1500mAh cells.
Eneloop (and all other brands of LSD cells) can be recharged using any good quality 'smart' NiMH charger. Depending on which charger you use, the charge time can be as short as 15 minutes, or as long as 8 hours.
[BOTTOM LINE]
The only verifiable benefit for PowerGenix NiZn cell is its higher operation voltage. However, even this may turn out to be a curse rather than a blessing, as higher voltage can cause unregulated appliances to burn out.
If you have a digital camera that works well with eneloop, stay with it. Switching to NiZn will not offer more power, nor longer run time. Only if your camera does not work well with eneloop, then it is worthwhile to try NiZn cells as a last resort. But you better contact PowerGenix, and ask whether they will assume warranty liability for the use in your camera. Otherwise, try it at your own risk!
[Update on Nov 21, 2010]
My first set of four NiZn cells was used for capacity testing and long-term self-discharge testing. They have gone though maybe 20-30 deep discharge/recharge cycles (discharged down to 0.9V only, not 0V) over the past year. As of right now, two out of four cells have already failed, suffering from voltage depression and rapid self-discharge problems. The other two suffered from reduced capacity (~1200mAh, down from the original 1500mAh). The PowerGenix '1-hour' charger needs to detect 1.9V during charging, before it can change from constant-current mode to constant-voltage mode. When voltage-depression hits a cell, its voltage cannot reach 1.9V during charging, so the NiZn charger will simply fry the cell!
18 of 18 found the following review helpful:
 Excellent for Pentax k100d Feb 10, 2010
By Tzvi D. Amsel
When I was still using Nimh batteries in my Pentax k100d camera, I was constantly switching out the batteries. The camera would shut off as the voltage dropped slightly, even though there was still plenty power available. Plus I was constantly buying new sets, as the problem gets worse as the set is used- even though there were very few recharge cycles used. That was because the camera needs minimum 1.2 volts to function. Well, Nimh is only rated at 1.2 volts. Unless new AND fully recharged, your not going to get that full 1.2 volts that are needed.It was the main thing pushing me to upgrade to a new camera that would use the more expensive lithiums.
However,thanks to the high 1.6 voltage on these Nizn batteries, I've been going on seemingly forever with one set. Plus my flash gun recycles way quicker (note: due to the quicker recycle time the flash can overheat if repeatedly cycled on full power without a break - do a web search). It's even been measured when fully charged to reach over 1.8 volts.
Note that the amount of recharges you can get will probably be less then with Nimh. Maybe more in line with Ni-cad. However, I don't see myself using that up for quite some time. Also note that you can't use a non-Nizn battery charger, so you'll need to buy a new PowerGenix charger as well.
A fantastic buy!
12 of 13 found the following review helpful:
Preliminary test are awesome! Feb 26, 2010
By James E. Clarke
So this is a preliminary test of the flash recycle times capable with these batteries.
I purchased 3 sets and compared them out of the package uncharged to Duracell and Energizer alkaline straight from package. Here are the results!
Recharge time 1/1 power, 5 shot average. 3 new sets of 4 batteries of each type were used to obtain average.
Flash: Nikon SB-24 Nikon SB-25 Vivitar 285 (non-HV)
Duracell 10.2 secs 10.9 secs 11.5 secs
Energizer 10.1 secs 11.0 secs 11.9 secs
POWERGENIX 2.2 secs 2.3 secs 3.3 secs
Obviously flash recharge times are far faster, I will be further testing the batteries tomorrow shooting the state swim championships. Check back for another review then.
9 of 10 found the following review helpful:
 Great product when working Sep 17, 2010
By Thomas Fischel
Great product when working. Great concept dating back to 1903?
Use in AA Maglite, walkway lights, remotes, PC mouse, Wx stations, etc.
I have had to send back 24 of the batteries. Failed to charge any more.
I have both slow and fast PowerGenix chargers.
Too many have died.
Amazon was kind enough to replace many of them.
Will not send them back for exchange any more, just take the loss and throw them away
as they fail.
9 of 10 found the following review helpful:
5 dead batteries after Wii and XBOX 360 usage May 02, 2010
By Kristopher L. Gainey
I've already tossed 2 of these AA batteries and now have another 3 that refuse to charge and show ~0.4v on my multimeter...this just after about 5 uses in Wii and Xbox controllers. I bought them because they're made from less toxic materials but if they're not going to hold up...I may be switching back to NiMh soon.
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