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(More customer reviews)The Powergenix ZR-PGX5HRAA-4B 5-Hour Fast Charger package is priced slightly cheaper than the one with an '1-hour' charger (PowerGenix ZR-PGX1HRAA-4B). Some people may feel that slower charging rate means less stress to the battery, hence better for its lifespan, but that's not necessarily true in this case.
The difference between charging rates of PowerGenix '1-hour' and '5-hour' chargers is not as great as the names suggest. The '1-hour' unit charges at 1500mA maximum, but only for 1-2 cells. For 3-4 cells the current is reduced to 700mA. So it takes about 2 hours (in constant-current mode) to charge 4 cells to 80%, and then another 30 minutes (in constant-voltage mode) to top-off the charge. The '5-hour' unit charges at 500mA for 2 or 4 cells. So it takes about 3 hours to charge to 80%, and then another 1-2 hours to top-off.
Does charging a NiZn cell at higher rate make its capacity deteriorate much faster? PowerGenix has not provided any data so far, so we can only estimate the effect based on data for NiMH cells. It is true that faster charging rate generally means shorter battery lifespan for NiMH cells. However, the penalty is most severe when charging at current greater than 1C. For example, '15-min' (4C) or '30-minute' (2C) chargers are very bad for battery lifespan. Between '2-hour' (0.5C) and '5-hour' (0.2C) chargers, the impact is negligible.
According to spec sheet for Rayovac 1800mAh NiMH AA cell: if a cell is slow-charged at 0.1C, its capacity will drop by 5% after 200 cycles. But if the cell is fast-charged at 1C, then the capacity will drop by 10% after 200 cycles (discharge rate=1C in both cases). The difference is small enough, so it is fine to choose an 1-hour charger to save some time.
In this particular case, the PowerGenix '1-hour' (actually more like a '2.5-hour') charger is a much better value than the '5-hour' charger, but not because of different charging rates. The real problem is that the '5-hour' unit can only charge in pairs. So if you start with two cells having different amount of charge in them, then one cell will be over-charged. Unlike NiMH cells which are very tolerant to over-charging, NiZn cells are not as forgiving when over-charged. That, is the real reason why this slower '5-hour' charger is more damaging in terms of battery lifespan.
[Update on Jan 31, 2011]
Here are some additional details on the charging process of NiZn cell, which should help to explain the fundamental flaw of this PowerGenix '5-hour' charger.
NiZn cells must be charged in a 2-stage process, similar to that for Lithium-ion rechargeable batteries:
- Stage 1: charge in constant-current mode (at a fixed 500mA in this case) until the voltage across each cell reaches 1.90V
- Stage 2: charge in constant-voltage mode (at a fixed 1.90V), while the current gradually decreases with time. Stop when current drops to below 10%, or when timer expires (5 hour in this case)
When two NiZn cells are charged in series, only their combined voltage is monitored during charging. The charger will proceed to stage 2 when the combined voltage has reached 3.8V. If the two cells have different amount of remaining charges in them (due to variation in capacities or self-discharge rates), then one cell voltage may have risen to 1.90V, while the other one is still at 1.80V. But the charger will not proceed to stage 2, because the combined voltage is still below 3.8V. So from this point on, the first cell will be overcharged, which subsequently lead to reduced capacity and lifespan.
Click Here to see more reviews about: PowerGenix ZR-PGX5HRAA-4B, 3-5-Hour Fast Charger with 4 AA 1.6v High Voltage Rechargeable Batteries (Green)
PowerGenix Fast Charger delivers an efficient charge at a great value. Charge your AA or AAA NiZn batteries in about five hours. Charges to 80% in 3 hours trickle charges to full in 5 Hours. Charges 2 or 4 AA or 2 AAA NiZn rechargeable batteries at a time (charge in pairs or all four). Features a built-in "switching" power supply which will automatically adjust to any voltage from 100-240VAC for international use. The PowerGenix Fast Charger is intended for use with eco-friendly NiZn batteries only. NiZn technology is perfectly suited for high-tech devices like MP3 players, digital cameras, toys, and LED lights. Experience the Power by making the change to cutting-edge, environmentally friendly PowerGenix NiZn Chargers and Batteries today!
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