Automotive & Travel Comparisons · Reviewed September 26, 2026
NOCO GB40 vs Schumacher SL1639 Lithium Jump Starter
Both are 12V lithium jump starters with a 1000-amp headline. NOCO rates the GB40 for engines up to 6.0L gas and 3.0L diesel with IP65 protection; Schumacher rates the SL1639 for up to 8.0L gas and 6.0L diesel.
Best for
Drivers selecting a rechargeable 12V jump pack for a compatible vehicle and wanting USB device charging plus an emergency light.
Probably not for
24V systems, unsupported battery chemistries, vehicles above the stated engine range, replacing a failed vehicle battery, or ignoring safe connection procedures.
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NOCO Boost Plus GB40
NOCO rates the GB40 as a 12V, 1000A lithium-ion jump starter for gasoline engines up to 6.0 liters and diesel engines up to 3.0 liters. Its UltraSafe design includes spark-proof connection and reverse-polarity protection. The 2.4-pound housing carries an IP65 water-resistance rating and rubberized over-molding. It can recharge USB devices and includes a 100-lumen flashlight with seven modes, including SOS and emergency strobe.
Pros
- IP65 water resistance and a published 2.4-pound weight give clear information for vehicle storage and handling.
- Spark-proof and reverse-polarity protections are explicitly documented for the clamp connection.
Cons
- The 6.0L gas and 3.0L diesel limits are lower than Schumacher's published engine ranges.
- USB recharging rather than a newer fast-charge standard may require more advance charging time.
Who it’s for: Choose it for the documented enclosure rating, lower engine range and UltraSafe connection protections. Skip it for engines above its stated limits.
Check NOCO Boost Plus GB40 on Amazon Paid linkSchumacher Electric SL1639
Schumacher identifies the SL1639 as a 12V portable lithium power pack and 1000 peak-amp jump starter. The manufacturer rates it for engines up to 8.0 liters gasoline and 6.0 liters diesel. The exact Amazon listing includes USB charging and an LED emergency light. It is positioned for cars, motorcycles, trucks, SUVs, boats and RVs when their voltage, battery type and engine size match the manual.
Pros
- The published 8.0L gas and 6.0L diesel ranges cover larger engines than the GB40 rating.
- USB power and an LED emergency light combine roadside functions in one pack.
Cons
- Schumacher does not present the same IP65 housing claim on the cited SL1639 documentation.
- Its engine-size advantage is a manufacturer rating, not evidence that any neglected or damaged battery will start.
Who it’s for: Choose it when the vehicle falls above NOCO's engine-size ceiling but within Schumacher's rating. Skip it when a documented IP enclosure rating is a priority.
Check Schumacher Electric SL1639 on Amazon Paid linkThe same 1000-amp headline does not create the same engine rating
NOCO states up to 6.0L gasoline and 3.0L diesel for the GB40. Schumacher states up to 8.0L gasoline and 6.0L diesel for the SL1639. Those limits are manufacturer compatibility guidance, not results from one shared cold-weather or battery-condition test, so the engine ranges are more useful than treating the matching 1000A labels as interchangeable.
Engine displacement is only one variable. Temperature, battery chemistry, battery damage, state of charge, connection quality and vehicle electronics all affect whether a jump succeeds. Choose within the manufacturer range and keep the pack charged according to its manual rather than assuming the largest number can overcome every battery problem.
Connection protections help, but the sequence still matters
NOCO explicitly documents spark-proof connection and reverse-polarity protection. The SL1639 also requires following its supplied connection and safety instructions. Protection electronics are not permission to attach clamps casually, use a pack in rain beyond its rating or work around a leaking, frozen, swollen or visibly damaged battery.
Verify a 12V system and a supported lead-acid battery before connecting. Turn off loads, identify positive and negative points, keep cables clear of moving parts, and follow the exact manual sequence for connection, start attempts and disconnection. If the battery type or remote jump points are unclear, consult the vehicle manual or qualified roadside service.
A stored jump pack needs its own maintenance routine
Lithium packs self-discharge and can be affected by very hot or cold storage. Check the charge indicator on a recurring schedule and recharge after use or as the maker instructs. Do not leave the pack loose where it can be crushed, punctured or contact metal objects. Replace damaged cables or a swollen pack rather than testing it during an emergency.
The NOCO publishes an IP65 enclosure rating, but that does not make connectors waterproof during use or make the unit suitable for immersion. The Schumacher should likewise be kept dry and protected. Store either pack where it can be reached safely, along with gloves, a light and the instructions.
Choose by vehicle compatibility, then by enclosure and charging
Choose GB40 when the engine fits its 6.0L gas or 3.0L diesel ceiling and the IP65 enclosure plus specified connection protections are valuable. Choose SL1639 when a compatible engine needs Schumacher's wider 8.0L gas or 6.0L diesel rating. Both can charge USB devices and provide emergency lighting, but those secondary functions consume stored energy.
Confirm the exact GB40 or SL1639 model in the Amazon listing because visually similar jump packs use different clamps, batteries and ratings. A jump starter is not a battery charger, battery tester or permanent fix for a failing charging system. After a no-start or repeated discharge, diagnose the battery and vehicle instead of relying on repeated boosts.
Official sources and further reading
Sources reviewed on September 26, 2026. Prices, availability and terms can change; recheck before buying.
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