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(More customer reviews)On first glance, the PowerGenix Nickel-Zinc Rechargeable Batteries seem to offer many advantages over ordinary rechargeable NiMH cells: higher voltage, higher energy density, lighter weight, longer cycle life, and so on. But before you rush to replace all your rechargeable batteries with NiZn type, let's examine each claim carefully to separate marketing hypes from technical facts:
"30% Higher Voltage" [FACT]
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!
"33% Higher Energy Density" [HYPE]
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
"30% weight and size reduction" [HYPE]
The weight of each NiZn AA cell (25g) is about the same as NiMH AA cell (27g for eneloop). For certain applications, it is possible to use three NiZn cells (3*1.65=5V) to replace four NiMH cells (4*1.25V=5V). But doing so also shortens run time by 25%.
"Longer Cycle Life" [HYPE]
PowerGenix claims that service life of NiZn cell 'meets or beats' that of NiMH cells. However, technical data found on PowerGenix web site says NiZn cell is rated for 200 cycles (at 100% deep-discharge), shorter than the 500-1000 cycles cited for most NiMH cells.
"Longer shelf life" [HYPE]
It is probably true that NiZn cell offers longer shelf life than Lead-Acid batteries (which are notorious for high self-discharge rate), but how does it compare against low-self-discharge NiMH cells? In the PowerGenix "Charging Procedure" section, it says you have to recharge the NiZn batteries once every 30 days!In summary, 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. For example, the light bulb in a typical two-AA flashlight is only rated for 2.3V. But a pair of freshly charged NiZn cells produce 1.85*2=3.7V, which is enough to burn out the bulb. If you intend to use those NiZn cells in your digital camera, make sure the latter is still covered by warranty!
Finally, NiZn cells cannot be recharged using ordinary NiMH chargers. You have to purchase the special PowerGenix ZiNc 4-Position Charger, and be careful not to mix up different types of AA batteries and chargers. So unless you are desperate for higher battery voltage, it is probably not worth the extra expense and risk.
[Update on Nov 21, 2010]
My original review was written more than one year ago. At that time, I was just pointing out the marketing hypes surrounding the release of this product. Since then, I also found NiZn cells to be very poor in terms of quality and longevity.
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!
Click Here to see more reviews about: PowerGenix PGX-4AAZiNc-1.6v High Voltage Rechargeable AA Batteries - 4 Pack
PowerGenix 4 Pack AA 1.6v High Voltage Nickel Zinc Rechargeable cells 2500 mWa
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