Pick a jump starter by engine, not by the biggest number on the box. The NOCO GB40 is rated for gas engines up to six liters and diesels up to three. The GB70 doubles the peak amps and covers gas up to eight liters and diesel up to six. The GB40 weighs about half as much and recharges in about three hours; the GB70 takes about seven. TechGearLab's April test named the GB40 its best compact jump starter.
Is the GB40's rating enough? Usually, yes. On a 33-degree day, TechGearLab's GB40 started a V6 Ford Explorer with a completely dead battery three times in a row, and that engine drew only about 300 amps. They also note there's no industry standard for peak-amp claims. Its catch is a small battery: in Car and Driver's test, one jump on a badly drained battery took it from full to about a quarter, and its leads are short. Check its charge every few months and recharge it after every jump.
The GB70 is the safer bet for big or tired engines. TechGearLab scored it higher for power, and it adds a 12-volt outlet for gear like a tire inflator. The trade-offs: about twice the weight, a slower recharge and a higher cost.
Both work the same way: red clamp to positive, black to negative, press power, then start the car. If it doesn't start, NOCO says wait 20 to 30 seconds and try again. Manual override turns the safety features off, so read the guide first. Skip both if your car's 12-volt battery is lithium; NOCO says these are for lead-acid only.
Winter tip: NOCO says to recharge between 32 and 104°F, so bring it inside rather than leaving it in a freezing garage. After a jump, Car and Driver suggests driving 15 to 30 minutes or putting the battery on a charger.
Our verdict: for most cars and crossovers, get the GB40. It's small enough to actually live in your car, and a great gift for a new driver or commuter. Full-size truck, V8 or diesel? Get the GB70.
