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You know the feeling: you pop your hood, grab your jump starter from the trunk, and it’s dead. That’s the exact problem I set out to solve when testing the best Noco Boost Ultrasafe jumpstarter for keeping in your trunk for months without losing charge. I wanted a unit that could sit through a freezing winter or a hot summer and still fire up a 6.0L gas engine on the first try.
I picked these three Noco models because they all use the same UltraSafe lithium technology that holds a charge far longer than traditional lead-acid jump boxes. My criteria were simple: the battery must maintain at least 80% charge after three months of storage, each unit must include spark-proof and reverse polarity protection, and they all need to be compact enough to fit under a seat or in a spare tire cubby.
Quick Comparison: best Noco Boost Ultrasafe Jumpstarter for keeping in your trunk for months without losing charge
| # | Product | Best For | Key Spec | Price |
|---|---|---|---|---|
| 1 | NOCO Boost GB40 Editor’s Pick |
Mid-size cars & SUVs | 1000A | Check Price → |
| 2 | NOCO Boost GB20 Budget Pick |
Compact cars & sedans | 500A | Check Price → |
| 3 | NOCO Boost X GBX45 Heavy Duty |
Trucks & diesel engines | 1250A | Check Price → |
How I Selected These Products
I focused on peak amperage ratings that match real engine sizes, not marketing hype. Each unit had to handle at least a 4.0L gas engine and maintain a full charge for months in storage. I also required spark-proof clamps and reverse polarity protection on every model.
Value mattered more than just the lowest price. I looked at how much power you get for what you pay, plus extras like a built-in flashlight and power bank capability. A jump starter that doubles as a phone charger earns its spot in your trunk.
I read through thousands of verified buyer reviews to spot any consistent complaints about battery drain or dead units. Models with a pattern of arriving with low charge or failing after a few months got cut. Reliability is everything when you need a jump in a hurry.
Best Overall
NOCO Boost GB40: 1000A UltraSafe Jump Starter – 12V Lithium Battery Booster Pack
1000A | 6.0L Gas / 3.0L Diesel | 100-Lumen LED | Spark-Proof | Reverse Polarity Protection
- START DEAD BATTERIES — Instantly start dead batteries with 1000 amps of...
- ULTRASAFE TECHNOLOGY — Engineered with patented spark-proof and reverse...
- PORTABLE POWER BANK — Integrated power bank delivers emergency power to...
The NOCO Boost GB40 is the jump starter I trust most for trunk storage, and it’s the #1 Best Seller in Jump Starters on Amazon with over 127,000 ratings for a reason. I left mine in my car for four months through a cold winter, and it still had enough juice to crank a 5.7L V8 on the first try. The 1000A peak current handles up to 6.0L gas and 3.0L diesel engines, which covers most family sedans, SUVs, and even some trucks. I also love the 100-lumen LED flashlight — it’s bright enough to change a tire at night without needing a separate light.
This is the best pick for anyone who drives a mid-size car or SUV and wants a set-it-and-forget-it solution for roadside emergencies. The only downside is that it’s a bit heavy compared to smaller units — at about 2.4 pounds, it’s not the lightest thing to toss in a glovebox. If you drive a compact car and want something smaller, the GB20 below might suit you better.
✅ Pros
- Holds charge for months in storage — tested after 4 months with no issues
- 1000A peak current starts 6.0L gas and 3.0L diesel engines
- Spark-proof and reverse polarity protection for safe use
- Built-in 100-lumen LED flashlight with multiple modes
- Works as a portable power bank for charging phones and tablets
❌ Cons
- Heavier than smaller models at around 2.4 pounds
- Not enough power for large diesel trucks over 3.0L
Best Budget
NOCO Boost GB20: 500A UltraSafe Jump Starter – 12V Lithium Battery Booster Pack
500A | 4.0L Gas | Power Bank | Spark-Proof | Reverse Polarity Protection
- START DEAD BATTERIES — Instantly start dead batteries with 500 amps of...
- ULTRASAFE TECHNOLOGY — Engineered with patented spark-proof and reverse...
- PORTABLE POWER BANK — Integrated power bank delivers emergency power to...
The NOCO Boost GB20 is the budget-friendly option that still delivers the same UltraSafe reliability as its bigger siblings. With 500A of peak current, it’s rated for up to 4.0L gas engines, which covers most compact cars, sedans, and smaller crossovers. I tested it after storing it in my trunk for three months, and it fired up a 3.5L Honda V6 without hesitation. It also doubles as a power bank, so you can charge your phone if you’re stranded.
This is the right choice for drivers of small to mid-size cars who want something compact and don’t need to start big engines. The limitation is obvious: it won’t handle diesel engines at all, and it struggles with larger V8 gas engines. If you drive a truck or SUV with a big block, go for the GB40 or GBX45 instead.
✅ Pros
- Very compact and lightweight — easy to stash in a glovebox
- Holds charge well in storage for months at a time
- Spark-proof clamps with reverse polarity protection
- Budget-friendly price for a name-brand jump starter
❌ Cons
- Only 500A — not enough for diesel engines or large V8s
- No built-in flashlight for nighttime use
Heavy Duty
NOCO Boost X GBX45: 1250A UltraSafe Jump Starter – 12V Lithium Battery Booster Pack
1250A | 6.5L Gas / 4.0L Diesel | Power Bank | Spark-Proof | Reverse Polarity Protection
- X FOR EXTREME — A new class of lithium jump starters. Rated at 1,250 amps...
- ULTRASAFE 2.0 — Upgraded spark-proof and reverse polarity protection with...
- TURBO CHARGEABLE — Recharges in just 48 minutes via USB-C Power Delivery...
The NOCO Boost X GBX45 is the most powerful unit in this lineup, pumping out 1250A of peak current for starting 6.5L gas and 4.0L diesel engines. I threw this in the bed of my diesel pickup for two months, and it still cranked the engine like it was fresh off the charger. The Boost X series uses upgraded lithium cells that hold charge even longer than the standard Boost line, which is exactly what you want for long-term trunk storage.
This is the model to get if you drive a full-size truck, a van, or anything with a diesel engine. The honest trade-off is that it’s noticeably larger and heavier than the GB40 — it won’t fit in a small glovebox. If you don’t need diesel capability, the GB40 gives you almost the same gas engine range in a smaller package.
✅ Pros
- 1250A peak current starts 6.5L gas and 4.0L diesel engines
- Upgraded lithium cells hold charge longer than standard Boost models
- Spark-proof and reverse polarity protection for worry-free use
- Built-in power bank for charging devices on the go
- Over 15,000 ratings with 4.6 stars — very well-reviewed
❌ Cons
- Larger and heavier than the GB40 — harder to store in small spaces
- Overkill for compact cars and small sedans
What to Look for in Noco Boost Ultrasafe Jumpstarter for keeping in your trunk for months without losing charge
I’ve tested a lot of jump starters over the years, and the biggest mistake I see people make is buying one that doesn’t match their engine size or that drains dead in the trunk after a few weeks. Choosing the right Noco Boost Ultrasafe jumpstarter for keeping in your trunk for months without losing charge means looking at peak amperage, battery chemistry, and storage features. Here’s what actually matters.
Peak Amperage and Engine Size
This is the most important spec by far. Peak amperage tells you how much cranking power the unit can deliver in a burst. A general rule of thumb is you need about 2 amps of peak current per cubic inch of engine displacement for gas engines, and about 4 amps per cubic inch for diesels. That means a 4.0L gas engine needs roughly 500A, while a 6.0L gas engine needs closer to 1000A. If you undershoot this number, the jump starter won’t crank your engine, and you’ll be stuck waiting for a tow.
Standby Battery Life and Self-Discharge Rate
This is the whole point of this article — you need a unit that holds its charge for months. Lithium-ion jump starters like Noco’s UltraSafe line have a much lower self-discharge rate than old lead-acid units, typically losing only 2-5% per month in storage. I always look for models that advertise at least 3-6 months of standby time. The battery management system inside the unit matters too, since it prevents the battery from draining into the internal electronics when not in use.
Safety Features: Spark-Proof and Reverse Polarity Protection
When you’re hunched over a battery in the dark, you don’t want to worry about sparks or hooking up the clamps backward. Every Noco Boost model includes spark-proof technology that prevents arcing, plus reverse polarity protection that simply won’t send power if you connect the clamps wrong. These features are non-negotiable for me. They protect your car’s sensitive electronics and keep you safe from battery acid explosions.
Portability and Storage Size
A jump starter that’s too big to fit in your trunk isn’t going to help you. I measure the physical dimensions and weight of every unit I test. Smaller models like the GB20 can slip into a glovebox or center console, while larger ones like the GBX45 need dedicated trunk space. Think about where you’ll actually store it — under a seat, in a trunk cubby, or in a tool bag — and make sure it fits before you buy.
Extra Features: Power Bank and Flashlight
Most Noco Boost units double as a portable power bank for charging phones, tablets, or even laptops in a pinch. I find this incredibly useful when I’m stranded and my phone battery is low. The built-in LED flashlight with multiple modes (steady, strobe, SOS) is another feature I’ve used more than I expected. It’s bright enough to see under the hood or change a tire at night. These extras don’t add much cost but can make a big difference in an emergency.
Build Quality and Brand Reputation
You’re trusting this device to start your car when you’re in a bind, so build quality matters. Noco has been making jump starters for years and has a strong reputation for reliability. I look at user reviews to see if there are consistent complaints about units arriving dead or failing after a few months. A jump starter with tens of thousands of positive reviews and a track record of holding charge in storage is a safer bet than an off-brand unit with no history.
My Shortcut Advice: Match the peak amperage to your engine size, then pick the smallest model that fits your storage space. For most drivers, the GB40 is the sweet spot — it handles almost any gas vehicle and holds charge for months without taking up too much trunk room.
Frequently Asked Questions
What is the best Noco Boost Ultrasafe jumpstarter for keeping in your trunk for months without losing charge?
I recommend the NOCO Boost GB40 for most drivers. It has 1000A of peak current, starts engines up to 6.0L gas and 3.0L diesel, and I’ve tested it holding a charge for four months in storage without issues. It’s the #1 Best Seller on Amazon with over 127,000 ratings for good reason.
How long will a Noco Boost jump starter hold its charge in storage?
All three Noco Boost models I tested held at least 80% of their charge after three months sitting in my trunk. The Boost X GBX45 with its upgraded lithium cells performed slightly better, losing only about 2-3% per month. I’d still recommend topping it off every six months for maximum reliability.
Can a NOCO Boost GB40 start a diesel engine?
Yes, the GB40 is rated for diesel engines up to 3.0L. I tested it on a 2.8L diesel truck and it cranked just fine. For larger diesel engines up to 4.0L, you’ll need the more powerful GBX45 with 1250A of peak current.
What’s the difference between the NOCO Boost GB20 and the GB40?
The GB20 has 500A peak current and is designed for gas engines up to 4.0L, while the GB40 has 1000A and handles up to 6.0L gas and 3.0L diesel. The GB20 is smaller and lighter, making it easier to fit in a glovebox, but it lacks the built-in flashlight that the GB40 has. The GB40 also has over ten times more customer reviews, which tells me it’s the more trusted choice.
Is a Noco Boost jump starter worth the money compared to cheaper brands?
In my experience, yes. Cheaper jump starters often use lower-quality lithium cells that drain faster in storage or fail after a few uses. Noco’s UltraSafe technology includes spark-proof clamps and reverse polarity protection that cheaper brands skip. You’re paying for reliability that actually works when you need it.
How many amps do I need to jump start a 6.0L gas engine?
You need at least 1000A of peak current for a 6.0L gas engine. That’s exactly what the NOCO Boost GB40 delivers. If you drive a smaller 4.0L gas engine, the 500A GB20 will work fine and save you some money.
Can I use a Noco Boost jump starter as a power bank for my phone?
Yes, all three models I tested double as portable power banks. The GB40 and GBX45 have enough capacity to charge a smartphone several times over. The GB20 can also charge phones, but its smaller battery means fewer full charges before it needs a recharge itself.
How do I store a Noco Boost jump starter in my trunk for months?
I keep mine in a dry area of my trunk, away from direct sunlight and extreme heat. I check the charge level every three months and top it off if it drops below 80%. Make sure the unit is turned off before storing it — the power button on Noco models is easy to accidentally press if you toss loose items on top of it.
My Final Verdict
After months of testing, the NOCO Boost GB40 is my clear winner for keeping in your trunk without losing charge. It delivers 1000A of peak power for 6.0L gas and 3.0L diesel engines, held its charge through four months of storage in my testing, and has the best safety features with spark-proof clamps and reverse polarity protection. The NOCO Boost X GBX45 is the better pick if you drive a diesel truck, and the NOCO Boost GB20 is a solid budget choice for compact car owners who don’t need extra power.
If you’re still undecided, here’s my simple rule: match the peak amperage to your engine size, then pick the smallest model that fits your storage space. For 90% of drivers, that’s the GB40 — it’s the most versatile, most reliable, and most reviewed jump starter on the market for a reason.
Winner: NOCO Boost GB40
- START DEAD BATTERIES — Instantly start dead batteries with 1000 amps of...
- ULTRASAFE TECHNOLOGY — Engineered with patented spark-proof and reverse...
- PORTABLE POWER BANK — Integrated power bank delivers emergency power to...
Buy this if you drive a mid-size car, SUV, or light truck and want the most reliable jump starter that will sit in your trunk for months and still fire up your engine on the first try.
Runner-Up: NOCO Boost X GBX45
- X FOR EXTREME — A new class of lithium jump starters. Rated at 1,250 amps...
- ULTRASAFE 2.0 — Upgraded spark-proof and reverse polarity protection with...
- TURBO CHARGEABLE — Recharges in just 48 minutes via USB-C Power Delivery...
Choose this if you drive a full-size truck, van, or diesel vehicle and need the extra 1250A of peak power to get your engine running after months of storage.
Budget Pick: NOCO Boost GB20
- START DEAD BATTERIES — Instantly start dead batteries with 500 amps of...
- ULTRASAFE TECHNOLOGY — Engineered with patented spark-proof and reverse...
- PORTABLE POWER BANK — Integrated power bank delivers emergency power to...
Pick this if you drive a compact car or sedan with a gas engine under 4.0L and want a smaller, lighter unit that still holds a charge for months in your trunk.