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(More customer reviews)This product (PowerGenix 4-Position Charger with 4 AA High Voltage 1.6v 2500 mWh ZiNc Rechargeable Batteries) contains an 'one hour' charger specially designed for Nickel-Zinc AA/AAA cells. But it does not fully recharge to 100% within one hour. If you read the fine prints, it actually says "For maximum capacity from batteries charge up to 2.5 hours".
Despite its misleading name, this is actually a decent 'smart' charger. It works from universal input voltage (100-240V), and accepts 1-4 AA cells or 1-2 AAA cells. Each cell is charged individually (not in pairs). The red LED lights up during charging, and the green LED lights up when done. Just remember that you must not use this NiZn charger for NiMH cells, and vice versa.
The batteries are the new Nickel-Zinc rechargeable AA cells. The greatest selling feature of NiZn cell is its higher terminal voltage. The nominal operating voltage of NiZn is 1.65V, which is very close to alkaline and 30% higher than NiMH (1.25V nominal). However, when freshly charged, the NiZn terminal voltage is around 1.85V, which is dangerously high for most battery-operated appliances.
Upon closer examination, many of the alleged benefits of NiZn turn out to be just marketing hypes. For examples:
"Higher Energy Density":
Despite what the confusing rating on the package ("2500 milli-WATT-hour") may suggest, the PowerGenix AA cell does NOT contain more energy than a SANYO eneloop AA cell. This is because its current capacity is much lower at just 1500 milli-Ampere-hour (based on data sheet of PowerGenix AA cell, and verified by my own testing).
- Energy in eneloop AA cell: 1.25V * 2000mAh = 2500mWh
- Energy in PowerGenix AA cell: 1.65V * 1500mAh = 2475mWh
As an example: Suppose a set of 4 eneloop AA cells can power your external flash unit for 1500 shots, then a set of 4 PowerGenix AA cells will provide roughly the same number of shots. The difference is that your flash unit will recycle about 30% faster with the NiZn cells due to 30% higher battery voltage. On the other hand, this high rate of fire could cause the flash to over-heat and burn out.
"Long Cycle Life":
PowerGenix claims that NiZn has a service life that 'meets or beats' that of NiMH cells. But according to technical data found on PowerGenix web site, the NiZn cell is only rated for 200 cycles at 100% deep discharge. Most NiMH cells are rated for 500-1000 deep discharge cycles.
"Long Shelf Life":
PowerGenix claims the NiZn cells have longer shelf life than Lead-Acid batteries (which are notorious for high self-discharge rate), but did not compare against NiMH cells. In the "Charging Procedure" section, it says to recharge the NiZn battery every 30 days!In summary: While the higher voltage offered by PowerGenix NiZn cells sounds attractive, it could damage or shorten the life span of your battery-operated appliances. In addition, NiZn cell does not pack more energy than eneloop NiMH cell, yet it suffers from lower cycle life and higher self-discharge rate.
On the other hand, suppose you have an inexpensive camera (*cough*Kodak*cough*) that does not work well with NiMH cells, then the higher voltage offered by NiZn cells may be exactly what you need. If your camera gets fried... oh well, at least you have an excuse to upgrade to a better camera!
[Update on Feb 9, 2010]
Several people have commented that my review above is heavy on technical data and not on personal usage experience. Please note that it was written shortly after NiZn AA cell was introduced. See my other review on PowerGenix ZRPGX-AA8 AA 8 Pack, which was written 3 months after this one. It includes my preliminary test results on self-discharge rate (good) and cell longevity (not so good).
Another point to note is that: since I'm an engineer, I'm overly concerned about applying 20% higher voltage (1.8V vs. 1.5V) to any electronic appliances. For example, I have tested my MAGLITE SP2209H 2-AA Cell Mini LED Flashlight over difference input voltage, and concluded that applying anything higher than 3.3V is dangerous (see my Customer Image for details). But other people may be happy to get extra light from higher voltage, without knowing that this can severely shorten the lifespan of the LED. Ignorance is bliss.
[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!
[Update Jan 31, 2011]
I recently discovered two other problems with the PowerGenix '1-hour' charger.
1. If a NiZn cell has been severely over-discharged and its voltage drops below 0.5V, the charger may not be able to detect its presence. If you insert this 'dead' cell together with three other good cells, the charger will not give you any warning signal (red LED flashing). But by the time the charger finished charging (green LED on), this dead cell is still empty. In this case, you need to use a 'dumb' NiMH charger to charge the dead cell for a few minutes, so that it can be recognized by the PowerGenix charger again.
2. If you store a set of fully charged batteries in this unplugged charger, each cell will be draining a current about 5.7mA into the charger. That means after about 10 days, all cells will be completely drained! With most other NiMH chargers I have tested, the leakage current is only 0.05-0.5mA, so you can store cells in them for several months without too much loss.
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PowerGenix – 1 Hour Quick Charger with 4 AA 1.6v Nickel Zinc high voltage rechargeable batteries 2500mWh
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