NOCO GB40 vs GB70: Which Jump Starter Fits Your Engine?

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Both the GB40 and GB70 come from NOCO's Boost UltraSafe line, share the same core safety features, and look nearly identical on a shelf. The decision between them comes down almost entirely to one thing: your engine size, plus whether you want a built-in 12V-out port.

Spec comparison

Prices are approximate at the time of writing and can shift with retailer promotions.

Decide by engine size first

The single most useful number on either spec sheet is the diesel rating, because it's where the two units diverge the most in practical terms. The GB40's 3.0L diesel ceiling covers smaller diesel engines but stops well short of a 6.0-6.7L Power Stroke, Duramax, or Cummins. The GB70's 6.0L diesel rating, by contrast, is built specifically for that heavy-duty truck-engine class. If you drive one of those larger diesels, the decision is effectively made for you — the GB40 isn't rated for that job, regardless of how appealing its lower price is.

On the gas side, the gap matters less for most drivers. The GB40's 6.0L gas ceiling covers the overwhelming majority of sedans, SUVs, and half-ton trucks on the road, and going up to the GB70 for a vehicle solidly inside that range mostly buys extra headroom rather than solving an actual sizing problem. That headroom isn't worthless — it helps offset the output loss lithium cells see in cold weather, covered in our winter jump starter guide — but it's a "nice to have" rather than a requirement for a typical gas vehicle.

The 12V-out port: the other real difference

Beyond peak amps and engine rating, the GB70 adds a 12V-out accessory port that the GB40 doesn't have. Per NOCO's documentation, this port lets the unit power 12V accessories — a separate air compressor, a cooler, a work light — independent of the jump-start clamps, turning the GB70 into a multi-purpose 12V power source rather than a single-function jump starter. If you want one device that jump-starts a vehicle and also runs other 12V gear, that port is a genuine feature difference, not just a marketing bullet point. Our guide to 12V-port jump starters covers this use case in more depth, including how it pairs with a separate inflator.

If your use case is strictly "start the car when the battery is dead, then put the unit away," the GB40 covers that job just as capably as the GB70 for a gas-engine vehicle, and the missing port isn't a loss since you weren't going to use it anyway.

Price versus what you're actually buying

The GB70 costs meaningfully more than the GB40, and that price gap buys three things: double the peak-amp ceiling, the extended diesel rating up to 6.0L, and the 12V-out port. For a diesel truck owner, all three of those are relevant and the higher price is simply the cost of the correct tool for the engine. For a gas-vehicle owner without a need for the 12V port, the price difference is mostly buying amp-ceiling headroom that a properly sized GB40 doesn't strictly need — a legitimate upgrade for peace of mind, but not a requirement.

Size, weight, and glovebox fit

The GB70's larger internal cell needed for its higher amp ceiling makes it somewhat bulkier and heavier than the GB40, which is worth factoring in if glovebox or console space is tight. This isn't a dealbreaker for either unit — both are still designed as portable, car-carried devices rather than shop equipment — but it's a real difference you'll notice day to day, especially if you're used to the smaller GB40's footprint and are considering stepping up primarily for headroom you may not need.

Shared safety features either way

It's worth noting that both units inherit the same UltraSafe design NOCO applies across the Boost line: spark-proof clamps and reverse-polarity protection, which prevent the two most common jump-starting mistakes — connecting the leads backward, or a spark near battery gases — from causing damage or injury. Neither of these safety features is exclusive to the pricier GB70; you're not paying extra for a safer unit, only for more amps, a higher engine-size ceiling, and the 12V port. That's useful to know if safety features, rather than raw capability, were the deciding factor in your mind, since both units are equally covered there.

The bottom line

Choose the NOCO Boost GB40 if you drive a gas vehicle up to a 6.0L engine or a diesel up to 3.0L, and you don't need a 12V-out port. Choose the NOCO Boost GB70 if you drive a 6.0-6.7L diesel truck — Power Stroke, Duramax, or Cummins — or you want the added 12V-out port for running other accessories off the same unit. When in doubt, size up: the GB70's extra headroom costs more but never leaves you undersized the way an underrated GB40 could on the wrong engine, and that margin is usually worth the extra money for anyone who tows, plows, or otherwise leans on their vehicle harder than an average daily commute.