How to Charge Die Hard Jump Starter—and Why a NOCO Boost Plus GB40 Lithium Jump Starter Fixed Our Shop

Last September, I sat in a customer's parking lot with a dead 2016 delivery van, a jump pack that clicked once, and the uncomfortable feeling that I'd taken a shortcut. The mistake actually started three weeks earlier, at the end of August.

I've been handling tool and equipment orders for our automotive shop for eight years (or rather, almost nine—the first year barely counts because I didn't know what I was doing). I've documented enough expensive mistakes to pay for a small vacation. The total is around $2,300 wasted budget. The jump starter bill was the most painful because it included a customer.

It Started With a Subwoofer and a Jack

In that same week at the end of August, I ordered two things for the shop that I'd been putting off for months: a Dayton Audio MX12-22 12" Max-X subwoofer for the stereo and a 2 ton Pittsburgh floor jack for the lift bay. Those were easy decisions. I'd owned similar models. The subwoofer and jack got the green light immediately.

The jump starter was different. For weeks I'd been comparing the NOCO Boost Plus GB40 lithium jump starter with cheaper units. Then the subwoofer and jack maxed out my monthly equipment budget. So I did the classic shop-manager move: I bought a cheap "600A" boost pack from a brand I now can't remember.

I should pause and be fair: that cheap unit isn't the villain. The villain is the idea that you can save money by ignoring the small print.

The Day I Searched "How to Charge Die Hard Jump Starter"

Fast-forward to a Tuesday morning in September. Our shop had a used Die Hard jump starter that came with a toolbox we bought at auction. No manual. I didn't trust it, but I didn't throw it out. While drinking coffee in the parts room, I typed "how to charge Die Hard jump starter" into my phone. I remember the exact search because it was the moment I realized we had no charging routine for any of our boost packs.

The internet gave me 30 minutes of conflicting forum advice. The only useful thing I learned was this: look up the exact model's charging procedure, and don't trust a green light until you know what it means.

Then the service call happened. A 2016 delivery van wouldn't start at a customer's lot. I grabbed that generic boost pack—not the Die Hard. The unit showed full charge. It turned the engine over exactly once. The second attempt was slower. By the third attempt, the boost pack was clicking and the van was dead silent.

We ended up telling the customer we'd send a tow. That tow cost us a $420 invoice we chose to eat, plus a conversation I didn't want to have.

Everyone had told me to check real cranking current instead of peak current. I didn't listen. I thought "600A peak" was enough. It wasn't. The lesson cost a service call, a customer relationship, and a $90 boost pack that went in the recycling bin.

What the NOCO Boost Plus GB40 Lithium Jump Starter Actually Does

After that call, I bought a NOCO Boost Plus GB40 lithium jump starter for the shop. It wasn't cheap. It wasn't magic. It was honest about what it could do.

Here's something jump starter vendors don't put on the front of the box: the big number is peak current, not cranking current. According to NOCO's product page—I checked it again in February 2026—the Boost Plus GB40 is rated for up to 6.0L gasoline and 3.0L diesel engines. The peak current is 1000A. That's the peak, not what the unit can feed a starter motor for ten seconds. The engine-size rating is what finally made sense to me: a lot more useful than a bold number on the front.

The second part of the fix was charging. I ordered a NOCO car charger—a GENIUS2—to keep the backup vehicle batteries and the roadside truck battery maintained. The GB40 itself tops up from a USB port in a few hours, and it's designed to sit on standby for months. But "designed to sit" isn't "always ready." We still set a monthly reminder to charge it.

So glad I checked the GB40's charge level before the next mobile job. I almost grabbed it out of the drawer the way I used to grab the old unit. It had enough charge, but the indicator told me I'd left it at 70% after the last use. If I'd ignored it, I'd have been in the same position—a jump starter can't jump itself when the internal battery is flat.

Now the honest caveats: the GB40 isn't the only jump starter we own. For the heavy diesel Sprinter in our fleet, we step up to a bigger NOCO model. And if a battery has an internal dead short, no jump starter in the world will crank it. You still need a good battery to start a vehicle; a jump starter is a way to deliver energy to a discharged battery, not a substitute for basic battery health.

The Old Rules and the New Ones

Ten years ago, most shop jump packs were lead-acid, and the best practice was to keep them plugged into a wall outlet. Lithium packs changed the conversation because they're lighter and hold charge longer. But they still need a charging routine. The fundamentals haven't changed: you need enough cranking power and a boost pack that's ready when the customer is waiting.

If you came here through the same "how to charge Die Hard jump starter" search I did, here's the short version: find the model number, get the manufacturer's manual, and follow its charging steps. If the manual is gone, call the company before plugging in an unfamiliar charger. Don't guess. And if a jump starter is more than a few years old, check the internal battery health rather than assuming it still holds a charge.

What I Keep on the Wall Now

The subwoofer and the floor jack are still in the shop. The jump starter I almost bought is not. The checklist I now keep above our charging bench looks like this:

• Look up the actual cranking current on the spec sheet, not the peak number on the front of the box.
• Match the pack to the largest engine you might face—ours covers up to 6.0L gas and 3.0L diesel; heavier trucks get a bigger unit.
• Know exactly how to charge the unit and how long it takes.
• Put a monthly charge reminder on the shop calendar, not on a sticky note.
• Write the purchase date on the pack. Lithium cells don't last forever.

The right tool isn't always the cheapest or the fastest to buy. It's the one you can trust to work when a customer is standing there waiting. That's what the NOCO Boost Plus GB40 lithium jump starter and the NOCO car charger did for us—and it only took one failed service call for me to learn it.