Schumacher Electric 1000 Peak Amp 12V Portable Lithium Car Battery Jump Starter & Power Pack - Lithium Ion Jump Box - with USB Charging & LED Emergency Light - SL1639

Why I started carrying this jump starter

A cold morning and a stubborn battery is all it took to make me rethink my emergency kit. I’ve been testing compact jump starters for years, and the Schumacher SL1639 has quietly become the one I keep in my glove box. It’s small, straightforward, and, most importantly, strong enough to crank real engines—not just lawn equipment.

Design and build

The SL1639 is a compact lithium-ion pack with a rubberized shell that feels ready for trunk life. It’s roughly the size of a thick paperback and light enough to toss in a backpack. The face is clean: a single power button, a simple charge indicator, a dedicated port for the smart jumper cable, and two USB outputs (2.4A and 3A). There’s also a built-in LED with steady, SOS, and strobe modes—more useful than flashy when you’re stranded at night.

The included smart clamps are better than the flimsy mini-clamps you see on bargain packs. The jaws bite well on side terminals and smaller posts, and the cable module incorporates the safety smarts: spark-proofing and protection against reverse hookup, short circuit, overcurrent, overload, and overcharge. Those protections matter, especially if you’re helping someone else and moving quickly.

Jump-start performance

What matters most is whether it starts vehicles without drama. In my tests, the SL1639 did exactly that. On a 5.3L V8 gas truck with a battery that had sat too long, it fired on the first try. On a 3.0L diesel SUV after a week in below-freezing weather, it turned the engine over confidently. The rating—up to 8.0L gas and 6.0L diesel—feels realistic as long as you’re not dealing with a severely sulfated battery or extreme cold that drags cranking amps way down.

The process is simple:

• Plug the smart jumper cable into the port on the pack.
• Attach red to positive, black to negative, ensuring a solid bite on clean metal.
• Press the power button on the pack.
• Wait a moment, then crank the engine.

I had best results cranking within 30 seconds of connecting. If the first attempt doesn’t catch, wait a minute between tries to protect the starter and the pack. As with any jump, switching off lights and accessories helps.

I’m always cautious about numbers, but this unit clearly has the guts you want. The jump is assertive rather than sluggish; you feel the starter motor spin up with confidence instead of the hesitant churn you get from underpowered packs.

Safety and user experience

Schumacher’s smart cable design does the right things quietly in the background. I intentionally mis-connected the clamps to test reverse-polarity protection; the pack refused to engage, and there were no sparks or heat. That’s table stakes these days, but not every budget pack gets it right. The spark-free design also means you can hook up without fear of arcing, which is reassuring in tight engine bays.

The single-button interface is easy but not fussy. Press to power on, hold to activate the light, tap to cycle light modes. Status indicators are basic—just enough to know your state of charge—but I never found myself guessing whether the unit was ready to go.

USB power and emergency lighting

Dual USB outputs at 2.4A and 3A are genuinely useful. The 3A port recharged my phone quickly, and the 2.4A port handled a tablet without complaint. This isn’t a weekend power station, but as a travel backup, it’s surprisingly handy. I used it during a power outage to top off a phone and a headlamp; it barely dented the charge level.

The LED light is brighter than most pack-in flashlights and throws a wide beam suitable for under-hood work. The SOS and strobe modes are there if you need to flag down help at night. In practice, the steady mode is what you’ll use most, and it’s good enough to change a tire or inspect a fuse box.

Battery life and recharge

The SL1639’s lithium-ion pack holds a charge well in storage. I left it in a trunk for a couple of months (checked once to top off), and it was ready when needed. As with all lithium packs, it’s smart to charge it every few months, especially if your climate swings hot or cold. Cold weather saps peak output; if you’re in subzero conditions, keeping the pack in the cabin rather than the trunk helps.

From empty, it recharges in about four hours with a decent wall adapter. If you use a weak adapter or a car USB port, expect it to take longer. That’s the one caveat: plan ahead. Don’t run it to zero, toss it on a random 1A charger, and expect it to be ready in an hour. I’ve had the best results giving it a proper wall charge after any jump-start.

What I’d change

• Faster top-off: Four hours from empty is fair for the capacity, but a higher input ceiling would shorten that with modern chargers. If you only have a low-power charger, it can feel slow.
• More detailed status: A simple percentage display would be nice. The basic indicator works, but precision helps you decide whether to top up before a long trip.
• Button feel: The power button works fine, but a slightly taller, clickier button would be easier with gloves—and less prone to feeling “squishy” in cold weather.

None of these are deal-breakers, and the core function—starting engines—remains strong.

Tips for best results

• Make clean contact: Clamp to the battery posts or a solid ground; paint and corrosion reduce current flow.
• Minimize loads: Turn off lights, blowers, and heated seats before cranking.
• Give it a breather: If your first start fails, wait 60 seconds before trying again.
• Store smart: Keep it out of extreme heat and, in winter, inside the cabin rather than the trunk.
• Maintain the charge: Top off every 2–3 months or after any use. A ready pack is the difference between a quick save and a tow.

Who it’s for

• Daily drivers who want self-sufficiency: If you’d rather not rely on jumper cables and a stranger’s car, this is the right size and power.
• Riders and weekend adventurers: Motorcycles, ATVs, and side-by-sides benefit from a small, robust pack that doubles as a charger and light.
• Light-duty fleets and farm use: It’s compact enough to keep in a glove box and strong enough for trucks within spec. For heavy equipment or repeated starts in a day, a larger unit is still better.

The bottom line

The Schumacher SL1639 hits the sweet spot for a portable jump starter: compact, confidence-inspiring power with sensible safety features and useful extras. It started every test vehicle I threw at it within its rated limits, the smart clamps are well designed, and the USB outputs and LED light make it a practical piece of kit beyond emergencies. Charge retention is solid, and while recharge time from empty isn’t lightning fast, it’s perfectly acceptable with a proper wall adapter.

Would I recommend it? Yes. If you want a reliable, glove-box-friendly jump starter that can crank anything from a small motorcycle to a full-size gas truck—and even mid-size diesels within spec—the SL1639 is a dependable choice. It’s not overloaded with gimmicks, it does the fundamentals right, and it adds just enough utility with USB charging and an emergency light to earn a permanent spot in your vehicle.