At some point in life, nearly every driver experiences the awkward and inconvenient situation of trying to start their car and failing due to an undercharged battery. If a vehicle is sitting for weeks or months, the battery may easily drain to a point where it won't turn the engine. While this can happen in any season, winter is especially tough on your car and extreme temperatures can cause the battery to fail to supply enough amps to the starter motor.

A portable jump starter is a lifesaver to get you where you need to go quickly and safely if there isn’t another driver around to give you a boost — or if you don't want to engage with a stranger while stranded. If the car battery is old won't hold a charge, a jump kickstarts the engine so you can drive to an auto store for a replacement. Ahead, we recommend the best portable jump starters and provide advice on what to look for while you shop.

Thankfully, portable jump starters are quite simple to compare to one another. These devices, sometimes called battery jump starters, are essentially heavy-duty backup batteries equipped with jumper cables, so take into account metrics like capacity, amperage, and interface ports.

Battery capacity is important because larger packs re-fire a greater number of vehicles and devices before they need to be recharged—bigger numbers equate to more capacity. Although some manufacturers measure battery capacity in terms of how many vehicles or devices it can charge, the standard unit of measure is milliampere hours (mAh). We recommend looking for jump starters that have at least 10,000 mAh of capacity, though you can get one that's nearly double that size, like our best overall pick.

Along with capacity, peak amperage is another important metric to look out for. This measures how much electricity the battery can supply in a given moment. More amperage generally leads to faster charge times and the ability to start bigger engines—as long as your vehicle can handle it. However, this is most relevant when starting your vehicle, as anything above 1,000 amps would fry your mobile device in an instant.

Outside of their main function, battery jump starters can also recharge phones, tablets, and other portable tech, so pay attention to interface ports. Most jump starters provide a number of USB ports, but the real kicker is to look for a 12-volt outlet. Along with faster charging, a 12-volt rail expands the range of devices that you’ll be able to power.

For the past five years, I’ve worked as an automotive journalist. In that time, I’ve tested a variety of vehicles and automotive products, including jump starters. Prior to becoming a journalist, I also worked in a garage, where our responsibilities often included testing batteries and jump starting dead ones. In my personal life, there have also been plenty of times that I’ve had to jump vehicles for myself or for others.

During the research phase, things like overall capacity, peak amperage, clarity of digital display, water resistance, and the number of ports factored into our decisions while making our selection, were just a few factors that helped inform our selection, along with price point.