This is truly an amazing device, fashioned of high-strength durable plastic, and photovoltaic cells that can charge several different sized batteries at once. The unit can recharge AA, AAA, C and D batteries, and does so extremely well. (The same model is also available here from a different seller.) It does take a while to recharge the batteries. Although in strong sunlight in a south-facing window, units can recharge in five or six hours, it can in winter sunlight or on cloudy days take much longer than that. However, once the batteries are charged, they tend to hold the charge for a long while --- several months in some cases, depending on their use.
We originally purchased this unit for camping. That turned out to be rather impractical, as many campsites are in shaded, forested areas. However, the purchase was worth every penny and over time has saved us a fortune in battery costs --- and no doubt quite a bit for electric-grid prices as well. Highly recommended. Solar 11-in-1 Battery Charger
I bought two of these recently. They do what they are supposed to do. I've used them to recharge Sanyo Eneloop batteries after I drained them in my Kodak digital camera. This battery charger works quite well. It uses sunlight to generate a current that charges pairs of batteries in sizes AAA, AA, C, or D. It will also charge gum batteries.
Sanyo Eneloop AA Battery 4 pack Precharged Use Up to 1500 Times
Kodak EasyShare C182 Digital Camera (Blue)
However, it will not recharge 9-volt batteries. The voltage from the solar panel isn't high enough. If you want to charge a 9V battery, the product you need is
AA and 9 volt battery charger with 3, 6, 9, and 12 volt power supply
The only thing the Crane charger's dial really indicates is current. The time shown on the dial is an estimate based on the assumption that the battery was drained until its pole potential difference was about one volt. It isn't the amount of time remaining. You still have to check the batteries from time to time with a voltmeter, until they're just over 1.4 volts each when you measure them with a voltmeter 30 minutes after taking them out of the charger. (The battery voltage usually falls off by 0.01V to 0.03V during the first half hour after removal.)
Not all of these chargers are equals. Some of them generate a higher charging voltage than others do. I tested mine with a voltmeter and found that one of them has a maximum voltage (full sun on perpendicular panel) of 5.4 volts, while the other shows 4.8 volts. As the result, the charger that creates the higher voltage charges pairs of batteries faster than the other one does. But both of them do charge pairs of NiMH batteries.
Added 21 April 2011. I bought a third charger. The voltage in full sun with panel normal is 5.2 volts.
Will a solar battery charger pay for itself? It depends on how you look at it. Versus buying lots of single-use alkaline or lithium batteries, definitely it will. Versus recharging batteries with a cheaper house-current powered charger, probably not. In 1500 rechargings of a pair of Eneloop batteries, you'll be lucky to get a dollar's worth of electricity out of them, at the present price of utility supplied electricity.
E = total energy
B = number of batteries = 2
R = number of rechargings = 1500
P = electric power
T = time
V = average battery voltage = 1.25V
E = BRPT = BR(IV)T = BR(IT)V
IT = 2000 mAh = 7200 amp-sec
E = (2 batteries)(1500 rechargings)(7200 amp-seconds)(1.25 volts)
E = 2.7e7 Joules = 7.5 kWh
Cost = 7.5 kWh ($0.1/kWh) = 75 cents.
Consider a solar battery charger to be a way to hedge your battery investment against the possibility that you might not have house current someday.
Added 21 April 2011. The maximum charging voltage for my best Crane charger is 5.42V. Once it has enough light intensity to reach this maximum voltage, further increases in light intensity no longer raise the voltage, but will raise the current flow. In full sun, with panel normal, the highest current flow I noticed was 0.180 amps. So the power being put into the batteries, at most, by the Crane charger is about 0.976 watts. This energy transfer rate will slow to about 0.457 watts as the two batteries, upon being charged, oppose their own voltage to that from the solar panel, assuming that the sunlight remains at a constant intensity and that the panel remains normal to the sun's direction during that time. If I approximate the average energy transfer rate by averaging the extremes of net voltage, it would take about 7 hours to fully recharge a pair of 2000 mAh AA batteries that had been completely discharged before recharging. In actual practice, you don't really fully discharge the batteries; you recharge them when their voltage has dropped so low (but not to zero) that they can't make anything work anymore, so it doesn't take as long as seven hours to top them off again.
Added 21 April 2011. Contrary to some of the reviews here, this charger will charge a pair of AAA, AA, C, or D size NiMH batteries on a cloudy day. The voltage from the solar panel on a cloudy day remains high enough to do the job.
Added 24 April 2011.
Assuming 1 volt potential difference across the poles of the battery.
Full sun: (5.4V-1.0V) x 180 mA = 0.79 W
Sunny w/ hazy sky: (5.0V-1.0V) x 150 mA = 0.60 W
Overcast by small cloud: (4.8V-1.0V) x 80 mA = 0.30 W
Strong overcast: (4.3V-1.0V) x 20 mA = 0.07 W
The charger works about 11 times faster on a clear day than it does on a strongly overcast day.
There's no need to weep and gnash your teeth in the outer darkness. With rechargeable low-self-discharge batteries and these solar battery chargers, you'll have power for your flashlights and digital cameras far into the die-off period of the Apocalypse. So stock up! - Battery Charger - C Crane - Solar Charger - Battery Chargers'
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