Just over 6 inches long, the PowerAll is a little big for most pockets, but easily stores in a car. PowerAll

The PowerAll measures 6.5 inches long, 2.9 inches wide, and only 1.2 inches thick. This lightweight brick includes a flashlight in one end, useful when fiddling around under the hood at night, and two USB ports. The package includes an AC adapter and a 12-volt DC adapter for charging at home or in the car, and a set of clamps to attach the PowerAll to a car battery.

The lithium ion battery in the PowerAll holds 12, 000mAh, but most important for jump starting a car, it cranks out 200 to 400 amps. I found multiple videos online of people jump starting big displacement V-8s with the PowerAll.

I got to try this one out personally when the battery in my BMW Z3 Coupe died. That's a 2.8-liter inline six-cylinder engine. I opened up the hatch and lifted a cover in the cargo area to find the battery, thoughtfully placed by BMW to avoid weather. I plugged the battery clamp attachment into the PowerAll, then attached the clamps to the battery terminals. In the driver seat, I turned the key and the engine cranked right up, as if it had a full charge.

Following PowerAll's instructions I immediately removed the battery clamps. And although it can reportedly handle about 20 jump starts, I took it inside and plugged it into the wall. PowerAll says it can handle more than 500 charge cycles, but should be plugged in once every three months to preserve the battery.

At 5.5 inches, the Jumpr can easily store in a glove compartment or coat pocket. Juno Power

Even more portable, Jumpr from Juno Power weighs only 7 ounces, about twice as much as an iPhone, and isn't much bigger. Its full dimensions are 5.5 inches long, 3 inches wide, and only 0.6-inch thick. The device includes a single USB outlet for charging phones and other devices, and the battery clamp attachment shown in the photo. Incidentally, this battery clamp is similar to that included with the PowerAll.

The capacity of its lithium polymer battery is 6, 000mAh, part of the reason why it is so much smaller than the PowerAll. However, it still can produce 300 amps for jump-starting a car. Juno Power's website claims it will work for most four- and six-cylinder cars.

Along with its small size, the Jumpr is also the cheapest of this bunch at $99. The Juno Power website notes the device is available for presale now at a special price of $69, with deliveries beginning in May.

The 14-ounce Versapower comes with cables for jump-starting and charging common portable electronics. Matco Tools

Those prone to trust a name brand may prefer Matco Tools' Versapower. This portable jump starter measures 6 inches long, 3 inches wide, and only an inch thick, and it weighs just 14 ounces. It also comes with an LED light, but just a single USB port. Included in the package is a battery clamp attachment along with a USB adapter ending in a 30-pin iOS device plug, a mini-USB, and a micro-USB.

Similar to the PowerAll, its lithium ion battery holds 12, 000mAh. Matco claims up to 1, 000 charge cycles for the Versapower. 300 cranking amps and a peak of 400 amps can handle jump starting V-8 engines. Matco Tools says the Versapower can jump start a Ford F-150 with a V-8 18 times on a single charge. As with most portable battery devices, it is a good idea to recharge the device every three months.