Editors' note: Portions of this review were copied from CNET's review of the Bolt Power D28 portable jump starter. The K3 Mini underwent similar testing.
Portable jump starters used to be a lead-acid car battery in a plastic casing, weighing up to 20 pounds. Now, improvements in lithium ion batteries enable a new breed of jump starter, one that can fit in your glove compartment and weighs about 10 ounces. Such is the BoltPower K3 Mini, a reasonably compact device that can rescue your car and also charge smartphones and other electronics.
At 6.75 inches long, 3 inches wide and well under a pound in weight, I could easily carry the K3 Mini around in one hand. It's a little big to fit in a pocket but would store in a car's glovebox or trunk easily enough. The K3 Mini comes in a zippered nylon case, holding its adapter and charging cables, which adds considerable size to the whole package. You might want to leave the case at home and just pack what's necessary in the car.
A black-and-gray plastic case gives the K3 Mini a modern look, and indentations along its body make it easy to hold securely. One long side holds two USB ports, a port for the jump-start battery clamp adapter, an LED charge level indicator and an electric input for charging the K3 Mini itself. A power button mounted on the top of the case turns on charging capability and also activates an integrated flashlight.
Cables included with the K3 Mini are the battery clamp adapter and a white multi-jack adapter with older and newer iOS plugs and plugs for Mini- and Micro-USB. In addition, BoltPower includes AC and 12-volt adapter cables to charge the K3 Mini.
To charge up my iPhone 5S, I had to plug in the white multi-adapter cable or my own iPhone cable, then press the power button. With the iPhone 5S plugged in and charging up, I attached another electronic device to the Mini-USB port on the same multi-adapter cable. Both charged simultaneously. Bolt Power marks one of the USB ports for 1 amp, and the other for 2.1 amps. The former will be suitable for most smartphones, while the latter is designed to charge tablets and larger electronic devices.
As the K3 Mini's battery is rated at 12,000mAh capacity, it could charge up my 1,900mAh iPhone 5S battery six times over. That amount of power is enough to charge a Nexus 7 tablet a couple of times, and can handle the latest iPad's 11,560mAh battery.
One of the K3 Mini's key features is its ability to jump-start a car. Unlike a typical portable battery backup just for charging devices, the K3 Mini comes with battery clamps that plug into a special port in its side. It can output a peak 400 amps, enough to jump-start a typical passenger car or truck engine up to a V-8.
To test the K3 Mini's jump-starting capabilities, I borrowed a Ford Country Squire station wagon with a 5-liter V-8. The car did not have a dead battery, so I took the positive battery cable off the battery. I attached the K3 Mini's black battery clamp to the car's negative terminal, and the red clamp to the positive battery cable. Turning the Country Squire's ignition key, the engine fired right up, as if it had a fully charged battery. Impressively, I fired up that engine another three times using the K3 Mini without stopping to recharge the device.
Finally, as a convenience feature, the K3 Mini includes a white LED flashlight integrated into its end. Turning it on involved pressing and holding the power button until the light came on. Pressing it again caused the light to flash, and once more set the flashing to a higher frequency. This flashlight would come in handy when fumbling around for your battery terminals at night, and the flashing light could serve in place of a flare.
The least-expensive of the Bolt Power portable jump starters, the K3 Mini lists for $119. This converts to around £74 or AU$135 for those ordering from the UK or Australia. However, Amazon, the only online store where I've found the K3 Mini sold, shows a price under $100. That is a reasonable price to pay for a device that can save you from waiting for a tow truck or good samaritan, especially as the device can also charge your phone.
I like the look and feel of the K3 Mini. The two USB ports make it convenient to charge multiple devices, and the included multi-adapter cable covers a wide variety of modern devices, certainly most that I carry. The blue LED charge indicator light isn't all that explicit about how much electricity is left in the K3 Mini, but it seems adequate.
The jump-starter battery clamp adapter's cables are a bit short, although they should be long enough for most applications. If a car battery has excessive infrastructure around it, the battery clamps might not reach the terminals, but it will work for the majority of cars on the road.