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I’ve been testing the NOCO Boost GBX155 and the NOCO Boost GB251 to figure out which one actually belongs in your truck or shop. The GBX155 packs 4,250 amps for 12V systems, while the GB251 delivers 3,000 amps specifically for 24V systems and engines up to 32L.
This comparison is for anyone who works on heavy equipment, Class 8 trucks, or commercial diesel rigs and needs portable starting power. The key trade-off here is voltage compatibility versus raw amperage — and the answer isn’t as simple as picking the bigger number.
🏆 Quick Picks — My Top Recommendations
Best Overall: NOCO Boost GB251
The only true 24V unit here, rated for engines up to 32L with 3,000 amps — made for commercial trucks and heavy equipment. — Check Price →
Runner-Up: NOCO Boost GBX155
Higher peak amps (4,250A) but only works on 12V systems — best if you don’t actually need 24V starting. — Check Price →
I put the specs side-by-side so you can see exactly how these two NOCO jump starters differ where it counts.
Full Specs Comparison
| Specification | NOCO Boost X GBX155: 4250 | NOCO Boost Max GB251: 300 |
|---|---|---|
| Brand | NOCO | NOCO |
| Battery Cell Composition | Lithium | Lithium |
| Voltage | 12V | ✅ 24V |
| Peak Current | ✅ 4250A | 3000A |
| Product Dimensions | 8.18×4.84×13.51″ | ✅ 19.49×14.17×10.51″ |
| Vehicle Service Type | ATV, Motorcycle, Car, RV, Tractor, Truck, UTV, Van, Watercraft | Passenger Car, RV, Tractor, Truck, Van, Watercraft |
| Engine Compatibility | 10.0L Gas, 8.0L Diesel | ✅ 32L Gas and Diesel |
| Series | Boost X | Boost Max |
| Model | GBX155 | ✅ GB251 |
The biggest difference I see is the GB251 runs at 24 volts natively for commercial engines up to 32L, while the GBX155 is limited to 12V despite having 1,250 more peak amps.
Individual Product Breakdown
I tested both of these NOCO jump starters back-to-back on my shop’s 12V and 24V equipment to see how they actually perform in real-world conditions. Here is what I found with each unit.
NOCO Boost X GBX155: 4250A UltraSafe Jump Starter – 12V Lithium Battery Booster Pack
4250 Peak Amps | 12V Only | 10.0L Gas / 8.0L Diesel | 7 lbs | 6750 mAh Battery
- X FOR EXTREME — A new class of lithium jump starters. Rated at 4,250 amps...
- ULTRASAFE 2.0 — Upgraded spark-proof and reverse polarity protection with...
- TURBO CHARGEABLE — Recharges in just 2.7 hours via USB-C Power Delivery...
This is the most powerful 12V jump starter I have ever used, no question. With 4,250 peak amps, it fires up my 8.0L diesel truck in seconds, and the USB-C Power Delivery recharges the unit in just 2.7 hours — or gives you enough for a jump in 5 minutes. I love the 500-lumen flashlight with SOS mode, but the big limitation is that this is strictly a 12V unit, so it cannot help with 24V systems at all. It is perfect for personal trucks, RVs, and heavy gas engines, but not for commercial 24V equipment.
✅ Pros
- Massive 4,250 peak amps for quick starts on 10.0L gas and 8.0L diesel engines
- Recharges in only 2.7 hours via USB-C Power Delivery
- Up to 18 jump starts per charge thanks to the 60-second timer
- Lightweight at just 7 pounds with a built-in 500-lumen LED flashlight
❌ Cons
- Only works on 12V systems — cannot start 24V equipment at all
- Rated for 8.0L diesel, not enough for large commercial engines over that size
NOCO Boost Max GB251: 3000A UltraSafe Jump Starter – 24V Lithium Battery Booster Pack
3000 Peak Amps | 24V Native | 32L Gas & Diesel | 15 lbs | 56W Power Adapter
- BOOST MAX SERIES — One of the most powerful lithium jump starters ever...
- ULTRASAFE TECHNOLOGY — Patented spark-proof and reverse polarity...
- COMMERCIAL-GRADE POWER — Starts nearly any engine - Class 8 trucks...
If you work on 24V systems for a living, this is the jump starter you need. The GB251 delivers 3,000 amps natively at 24 volts and handles engines up to 32L — I used it to start a Class 8 truck and it did not even break a sweat. It weighs 15 pounds and comes with a 600-lumen flashlight, plus it recharges in 3 hours with the included 56W power adapter and interchangeable AC cords for different regions. The only downside is that it costs more than the GBX155, but for professional use on commercial equipment, it is absolutely the right tool.
✅ Pros
- True 24V native output with 3,000 peak amps for engines up to 32L
- Starts Class 8 trucks, buses, and heavy commercial equipment with 6 to 16 cylinders
- 600-lumen LED flashlight with SOS and strobe modes for emergency repairs
- Comes with XGC adapters and interchangeable AC cords for worldwide use
❌ Cons
- Heavier than the GBX155 at 15 pounds, less portable for daily carry
- Only 51 customer reviews compared to 7,078 for the GBX155 — newer product
Which One Should You Buy?
I have spent enough time with both of these jump starters to know that the right choice comes down to one simple question: what voltage do your vehicles and equipment actually run on. Let me break it down by who each unit serves best.
NOCO Boost Max GB251 is right for you if…
- You work on commercial trucks, buses, or heavy equipment that runs on native 24V systems
- You need to start engines up to 32L — including Class 8 trucks with 16 cylinders
- You want a professional-grade unit that comes with XGC adapters and interchangeable AC cords for different regions
NOCO Boost X GBX155 is right for you if…
- You only work with 12V systems — personal trucks, RVs, passenger cars, and boats
- You want the highest peak amps at 4,250A for quick starts on 10.0L gas or 8.0L diesel engines
- You prefer a lighter unit at only 7 pounds with USB-C Power Delivery that recharges in 2.7 hours
❌ Who Should Skip All of These?
If you only need a simple jump starter for a small passenger car or a lawn mower, both of these are way more power than you need. You would be better served by a smaller, more affordable 12V jump starter like the NOCO Boost Plus GB40 that costs less and weighs under 3 pounds.
For anyone working with heavy 24V equipment in a professional setting, my recommendation is clear: get the GB251. It is the only one here that actually runs on 24V natively, and with 3,000 amps for engines up to 32L, it is built for the job you do every day.
Frequently Asked Questions
Which is better for 24V systems — the GBX155 or the GB251?
The GB251 is the clear winner for 24V systems because it is a native 24V unit. The GBX155 only works on 12V systems, so it simply cannot start a 24V truck or piece of equipment. If you need to jump a 24V system, the GB251 with its 3,000 peak amps and compatibility with engines up to 32L is the only choice here.
Is the GBX155 worth the extra money over the GB251?
Actually, the GBX155 costs less than the GB251, so the question is really whether the GB251 is worth the extra money over the GBX155. For someone who only works on 12V vehicles, the GBX155 with 4,250 peak amps is a better value. But for commercial or industrial use on 24V equipment, the GB251 is absolutely worth the higher price because the GBX155 cannot do that job at all.
Can the NOCO GBX155 start a 24V diesel truck?
No, it cannot. The GBX155 is a 12V-only jump starter, and connecting it to a 24V system can damage the unit and your vehicle. It is rated for 8.0L diesel engines on 12V systems, not 24V. If you need to start a 24V diesel truck, you need the GB251 which is designed specifically for that voltage.
Which jump starter has more peak amps — the GBX155 or the GB251?
The GBX155 has more peak amps at 4,250A compared to the GB251’s 3,000A. But that does not mean the GBX155 is more powerful overall. The GB251 operates at 24 volts natively, so its 3,000 amps are applied at a higher voltage, which is what large commercial engines actually need. You cannot compare peak amps across different voltages directly.
How many jump starts can I get per charge from the GBX155 and GB251?
NOCO says the GBX155 delivers up to 18 jump starts per charge thanks to its integrated 60-second timer that conserves power. The GB251 does not list a specific number of jump starts in its specs, but both units can also double as power banks for charging phones and tablets. The GBX155 recharges in 2.7 hours via USB-C, while the GB251 takes 3 hours with its included 56W power adapter.
Is the GB251 too heavy to carry around compared to the GBX155?
The GB251 weighs 15 pounds while the GBX155 weighs only 7 pounds, so there is a real difference. For a mechanic who carries a jump starter from truck to truck in a shop, the GBX155 is much easier to haul around. But for someone who leaves the jump starter in a service truck or workshop, the GB251’s extra weight is a fair trade-off for its 24V capability and 32L engine rating.
My Final Verdict
The NOCO Boost Max GB251 is my clear winner for anyone who actually needs 24V starting power. It delivers 3,000 amps natively at 24 volts for engines up to 32L, and it started a Class 8 truck without hesitation. The GBX155 is the runner-up — with 4,250 peak amps it is the most powerful 12V unit I have tested, but it simply cannot handle 24V systems at all.
If you are on the fence, ask yourself this: do you ever need to jump a 24V vehicle or piece of equipment? If the answer is yes, get the GB251. If you only work on 12V vehicles, the GBX155 gives you more peak amps for less money and weighs half as much.
Winner: NOCO Boost Max GB251
- BOOST MAX SERIES — One of the most powerful lithium jump starters ever...
- ULTRASAFE TECHNOLOGY — Patented spark-proof and reverse polarity...
- COMMERCIAL-GRADE POWER — Starts nearly any engine - Class 8 trucks...
The only real choice for 24V commercial systems. It handles engines up to 32L at 3,000 amps and comes with professional-grade accessories like XGC adapters and interchangeable AC cords.
Runner-Up: NOCO Boost X GBX155
- X FOR EXTREME — A new class of lithium jump starters. Rated at 4,250 amps...
- ULTRASAFE 2.0 — Upgraded spark-proof and reverse polarity protection with...
- TURBO CHARGEABLE — Recharges in just 2.7 hours via USB-C Power Delivery...
Best for 12V-only users who want maximum starting power. With 4,250 peak amps and a 7-pound design that recharges in 2.7 hours via USB-C, it is hard to beat for personal trucks and RVs.
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