Introduction
There have been external digicam power packs available on the market for quite a while now, but the recent release of a number of more power-hungry cameras has renewed interest in the category. After receiving a number of emails from readers asking about external power solutions for the Minolta Dimage 7, we took a look at a couple of PowerEx models from Maha. In the case of the Dimage 7, the Li-Ion version of the "PowerBank" product is the only solution we're aware of that powers the camera reliably. Here's what we found when we looked at the PowerEx PowerBank external battery packs, including a few usage & compatibility notes.

In the Box
Both models of PowerBank come equipped with a coiled power cable to connect it to your camera and a set of three adapter plugs that should suffice to mate it to just about any camera out there. Recharging is provided for through the usual wall-plug AC adapter, as well as a cigarette lighter adapter for use on the road. An attractive leatherette carrying case has a clip for attaching it to your belt.

Two models of the PowerBank are available, a NiMH-based one, and a LiIon one. Which you choose will depend on the power requirements of your camera. Both models are quite light, weighing only a few ounces.

Use
The PowerBanks are designed to plug into the external power jack of your digicam. The cord exits at a right angle, letting it hang down out of the way with most cameras. - The shot above shows it plugged into a Nikon Coolpix 995, with the cord coming straight down next to the hand grip, a very convenient arrangement.

There's not a lot to it, you just plug it in and go. Cameras will differ in how they behave when power is supplied via the external jack. With some cameras, plugging in the external jack physically disconnects the internal batteries, so once the PowerBank runs down, you can unplug it and the camera's internal batteries will take over. Some cameras will run from the external power source until the voltage drops to equal the internal pack, at which point it begins drawing from the internal batteries as well. On these cameras, you'll get a long overall run time, but when the power stops, the internal batteries and the PowerBank will both be drained.

A few cameras use the small LiIon rechargeable batteries, and having a power adapter voltage of 5.0 volts. These are a bit of a special case (see below), and you'll perhaps want to remove the internal battery when running from the PowerBank and carry it in your pocket as a spare. - Nothing serious, just a measure to get maximum run time. - See the additional information below.

Two Versions - NiMH and LiIon
As we mentioned above, there are two different versions of the PowerBank, one using NiMH battery technology, the other using LiIon cells. The two carry different mAh ratings (1800 for the NiMH, 1400 for the LiIon), but in actuality, they provide very close to the same total power capacity. This is because power is the product of voltage*current, and the LiIon pack delivers 7.2 volts, vs 6 volts for the NiMH. Thus, the net power comes out to 10.8 watt-hours for the NiMH pack, and 10.1 for the LiIon. Pretty close.

The determining factor in deciding which pack you need will be the terminal voltage demanded by your digicam at its external power jack. Most cameras these days are labeled right next to the jack, telling you what voltage they expect. For the most part, cameras will cheerfully tolerate slight over- or undertakes, but some caution is called for in going too far from manufacturer's specs. At the same time, some cameras labeled for 6 volt power may actually need the higher-voltage LiIon PowerBank to function properly. (A case in point being the Minolta Dimage 7 mentioned at the beginning of the article. - The flap over its power jack says "DC In, 6v", but it actually won't run reliably with the 6 volt PowerBank, instead needing the nominal 7.2 volts delivered by the LiIon version.)

Most digicams that use a set of four AA batteries will be candidates for the NiMH battery pack, with some exceptions such as the Dimage 7 (and its lower-res sibling the Dimage 5). A number of cameras are now using higher-voltage LiIon packs internally, and those will generally work with the LiIon PowerBank. (The Nikon 880, 885, 990, and 995 being notable examples.)

In general, you'll want to match the pack voltage to the voltage of your camera's AC adapter. Going forward though, we're going to try to consistently test new cameras coming through our lab against both pack types, to determine which pack they need.

5v-only cameras
We mentioned above that there were some cameras on the market that use small LiIon rechargeable batteries. (These batteries are known under a variety of model numbers, but NP-80 is one of the most common. - For reference, a Fuji FinePix 4800 Zoom is shown at right with the battery extending from the case slightly.) Cameras based on these batteries tend to have battery-charging circuitry built into the camera body itself, and require a 5v external power source.

This is a lower terminal voltage than most cameras on the market, and is lower than either PowerBank model supplies. Maha's solution is to offer a "step down" cable that drops the voltage of the NiMH PowerBank enough to safely power a 5v camera.

In our testing, we decided that the step-down cable is a bit of a qualified success: It did indeed work with the 5v cameras we tested it with, and does provide longer run times than you'd get from the cameras' internal batteries. You do end up with less run time than you'd normally get from the NiMH PowerBank on a camera with similar power consumption without the step-down cable though. This is because the step-down element inside the cable (a diode?) dissipates power in the process of stepping-down the voltage. This passive power loss essentially "throws away" a portion of the PowerBanks capacity. (Assuming the step-down device is a silicon diode, we calculate the power loss at about 1.25 watt-hours.) This power loss is evidenced by a slight warmth in the plug end of the cable when your camera is operating.

Another consideration when running 5v cameras from a PowerBank: We noted that these cameras have battery-charging circuitry built into them. This means that these circuits will potentially draw power to charge the internal batteries whenever they're connected to an external supply. Since battery-charging circuits aren't 100% efficient, drawing power from the PowerBank to charge the internal battery is probably a poor bargain. For best results then, we recommend removing the internal battery from these cameras when running from the PowerBank. When the PowerBank runs low, plug the internal battery back in and operate as normal.

"Gas Gauge"
One of the things we really like about the PowerBanks is the provision of a "gas gauge" on them, to let you know how empty or full they are. Pressing the small black button on the top of the unit lights from one to four LEDs, showing the PowerBank's state of charge. This is super-handy when you're in the field, wondering how much power you have left in the pack. It's also handy if you have a unit that's been sitting on the shelf for a while and you're not sure how fully charged it might be.

That said the gas gauge LEDs are only somewhat useful/accurate on the NiMH model. We suspect this is because terminal voltage is pretty tough to translate into charge status with NiMH batteries. In testing our units, we found that a *just* charged NiMH pack would show four LEDs, but even a tiny amount of use (or just sitting around for a few hours) would generally extinguish one of them. Thus, for the NiMH version, figure that 3 LEDs corresponds to a "full" condition. By contrast, the LiIon gauge seemed pretty representative of how much juice was actually left in the pack. (Although we didn't test for this explicitly.)

Charging
The PowerBanks are charged by plugging them into the provided AC adapter transformer, or the auto adapter. Both units will recharge from "dead" to "full" fairly quickly - 4 hours in the case of the NiMH version, 3 hours for the LiIon. The LiIon charger seems pretty intelligent, as the PowerBank doesn't get overly warm once it's fully charged. The NiMH charger appears to continue delivering a fairly high current to the cells though, as the pack gets quite warm once full charge is reached. We'd recommend putting it on a 5-hour timer to prevent overcharging, or possibly using an adapter with one of Maha's own more intelligent chargers, like the C-777.

Capacity/Run Time
This is a case where the phrase "your mileage may vary" will definitely apply. Besides the obvious differences in camera power consumption, the threshold or cutoff voltage below which the camera stops operating varies quite a bit from model to model. Some nominally 6 volt cameras will run on external power as low as 4.5v or less, while others will cut off well above 5v. In general, the PowerBanks will add about as much run time to a camera as an internal battery of similar mAh rating would provide. - This is perhaps a slightly conservative estimate, since their terminal voltages are higher than the internal batteries in most cases, so the current drain should be less. Countering this though, is that there are sometimes losses in the internal circuitry between the power terminal and the camera's electronics, such that you don't get the full benefit of the higher external voltage.

Bottom line, it's hard to get a get a firm answer on runtime without explicitly testing the camera with the pack. In the cases that we did test though, the PowerBank used in conjunction with the camera's internal batteries always doubled or more than doubled the run time. In the case of the Nikon Coolpix 995, we found that the LiIon PowerBank ran the camera for 4 1/2 hours all by itself, for a total time with the internal battery of 6 1/2 hours. (!) That's a very worthwhile extension!

Cost
The NiMH PowerBank sells for a list price of $59.95 (about $50-55 "street" price), while the LiIon version sells for $69.96 (about $60-65 "street" price). Click here to buy a PowerBank from a Maha-authorized distributor, or here for more information from Maha.

Bottom Line
With larger pixel counts and more sophisticated onboard processing, power consumption for high-end digicams has been holding constant or increasing, despite other technology advances. If you need to get really long run times from your camera, an external pack like the PowerBank could be just the ticket!

Purchase/More Info
Here's a link to a Maha/PowerEx distributor, with a good price on the PowerEx PowerBanks. For more info, here are some links to the Maha/PowerEx site: