Choosing a Portable Jump Starter: Engine Size, Safety Features and Upkeep

A jump starter is a portable battery that starts your car right now, wherever you are, without a second car. A battery charger or maintainer, like the NOCO GENIUS5, plugs into a wall outlet and recharges or maintains the car's battery over hours, which is what you want for a car that sits for weeks or a battery that's getting weak.

If your car only fails to start after a cold night or a light left on, a jump starter is the right tool. If it happens again and again, the battery or the charging system needs checking; a jump starter will keep getting you going without fixing the cause.

Use the maker's engine rating, in liters, rather than the peak amp figure on the box. Diesel engines need more power than gas engines of the same size, so their limit is lower. Check your engine size in the owner's manual or on the registration, then pick a model rated above it.

The common mistake with jumper cables is connecting the clamps the wrong way round. Look for reverse polarity protection, which stops the starter from sending power if the clamps are reversed, and spark-proof clamps. NOCO lists both on the GB40, GB50 and GB70.

Water and dust resistance help too, since you'll use it outdoors in bad weather. NOCO rates these three models IP65. All three also work as a USB power bank for a phone and have a built-in flashlight.

A jump starter that's flat when you need it is no help. Charge it fully when it arrives, keep it in the car, and check its charge level every few months, especially before winter. NOCO's GB40 recharges over USB-C in about three hours at 2.1 amps.

• Worth buying: anyone who drives alone, parks outdoors in cold weather, or has an older battery.
• Get a bigger model: big V8 trucks and diesel engines above the GB40's rating.
• Get a charger instead, or as well: cars, motorcycles and mowers that sit unused for weeks.