GOOLOO GT4000S 4000A SuperSafe Jump Starter

The GT4000S is for drivers who need truck- and diesel-class starting power without paying for a premium brick. Gooloo rates it for 12 V gas engines up to 12.0 L and diesels up to 10.0 L, the highest ratings of any pack on our list, which covers full-size pickups, work vans, RVs on a truck chassis, tractors and most boats. Outdoor Life picked it as its best jump starter for diesel trucks, noting that the diesel mechanics it consulted recommended it without hesitation. CNN Underscored names it one of its two top picks for 2026, alongside the NOCO Boost Plus GB40.

Recharge speed is the headline. The manual gives about 1.2 hours from empty to full on a 100 W USB-C PD charger, and Gooloo says five minutes of charging is enough for one emergency start. The box includes a 100 W car charger, which the manual names as one of the two ways to reach the full input rate; a smaller USB-C charger also works, more slowly. Among our other picks, only the HULKMAN Alpha85 comes close, at about 90 minutes on 65 W.

Peak-amp claims are not measured to a common standard, so the engine rating is the number to compare, and on that the GT4000S has more headroom than anything else here; the manual adds an 800 A starting current. A BOOST button forces output when the vehicle battery is too flat to detect, and the manual says more than four starts within ten minutes puts the pack in a safe mode for ten minutes.

The pack is rated IP65 against splashes and dust, though the manual is clear that it must not be submerged. A 3.2 in screen shows the charge percentage, a READY prompt when the clamps are on correctly, a warning for reversed clamps, and error codes for temperature and overcurrent. Outdoor Life singled out the large display as easy to read.

As a power bank it offers 100 W USB-C for a laptop, two USB-A ports, and a 15 V 10 A DC socket rated for 150 W that can run a socket pump from our best portable tire inflators list if its draw fits.

The paperwork is less consistent than it should be. The current manual on Gooloo's site lists a 74 Wh battery (5,000 mAh at 14.8 V), which matches the 20,000 mAh on the amazon.com listing. An earlier edition of the manual, hosted on ManualsLib, lists 99.2 Wh, and Outdoor Life quotes 26,800 mAh, so older stock may differ. Gooloo's product page also gives two engine ratings: 12.0 L gas and 10.0 L diesel in its headline and spec graphic, and 10.0 L gas and 8.0 L diesel in one paragraph lower down. We use the figures the manual prints, but if your engine sits near the top of the range, plan on the lower pair.

The safety standard has the same problem. The earlier manual edition prints "conforms to UL STD.2743"; we did not find that line in the text of the current edition, and the amazon.com listing names CE and FCC. That is less clear-cut than Hulkman's written UL statement for the Alpha85.

Size is the physical trade-off. Gooloo does not publish a weight, and Outdoor Life lists size among the cons. At 9.05 by 3.93 by 2.12 in, it is longer and thicker than the GB40 at 7.7 by 3.2 by 1.7 in, so it belongs under a seat or in a door bin rather than the glovebox.

Cold-climate owners should know that the manual reserves battery pre-heat for the GT4000; the GT4000S works from -4°F to 140°F and should only be charged between 14°F and 113°F. The manual gives an 18-month warranty, while Gooloo's US store advertises up to 30 months, so check the terms where you buy.

The NOCO Boost HD GB70 is the premium choice for big engines. It is rated lower (8.0 L gas, 6.0 L diesel), weighs 4.18 lb by NOCO's figure and takes 6 to 8 hours to recharge over USB, but it brings NOCO's clamps and a longer record in independent tests.

The HULKMAN Alpha85 is the closest match in features: a screen, IP65, fast USB-C charging and a 15 V DC port, plus a written UL statement and a published 2.57 lb weight, but lower ratings (8.5 L gas, 6.0 L diesel). For a big diesel the Gooloo has the margin; for a V8 gas pickup either will do. The full ranking is in our best portable jump starters list.

Buy the GT4000S if you need to start big gas or diesel engines, want a pack that recharges in just over an hour, and value an IP65 housing and a status screen in the budget class. Skip it if you want the smallest pack for a sedan, need a published weight or a UL 2743 line in the current manual, or live where winters routinely fall below the pack's -4°F floor, where a pack with battery pre-heat is the better tool.