Lithium jump start packs that don't suck?

Having just returned one that failed at the one job it has, in my book…

I want a lithium jump start pack, the dumber the better. If I hook it to a dead battery, I want it to put in a solid effort to charge it and get voltage up, not just clicking off. And if I hook it to a disconnected set of battery terminals, I want it to put ~14V on the terminals, and supply as many amps as it possibly can into that load, even with no 12V battery in the way.

The one I had failed at both of these, though I’ve seen others of various brands succeed at it (I didn’t take note of what said brands were, unfortunately).

In an ideal world, it could cold start a 7.3 Powerstroke with no batteries present, but I also don’t want to drop $500 on it…

lead acid does have a max charge rate to consider; you don’t want to boil off your water into hydrogen. sulfuric acid sprayed about due to hydrogen explosions are bad. That said, jumper cables should have about 1 ohm resistance between the connectors and cable length, so that’s a potential workaround. Then wait about 5 minutes for the battery to charge (i.e. if the battery isn’t completely toast), then try starting. I have to do that a lot when trying to jump start trucks with my little car; have to rev up high enough to charge and do that for 5-10 minutes before it’ll work.

As long as you limit the maximum voltage when charging things, you shouldn’t get much gas production - it’s a problem of voltage, not current. Though a large current source will cause a spike in voltage (this is why older generator based charging systems have high/low controls on the brush - if you’re running a tractor at low RPM, you need “more from the generator” than when you’re plowing at high RPM for hours on end, and the same adjustments go if you’ve got lights to run).

I can tell you that the most expensive POS at Autozone ain’t worth crap, it’ll happily kill itself (to the point where I could smell it getting melty inside) trying to charge a really dead battery.

A forum like this might be a place to start: Weego jump starts - General Equipment - but I bet the more expensive ones have safety features (but the really expensive ones you can bypass them).

I’m kind of OK with that, if it’s going to actually try to start a dead car!

I suppose I ought to just get some 26650 LiFePO4s and build my own…

I gave up on jump start packs because all batteries fail after a few years whether used or not. LiIo packs just cost more to do the same thing as SLA/Gel, but lighter. And as the Chinese have been cost-cutting like mad to deal with tariffs and high shipping costs, most are complete crap.

Now I have a $90 Schumacher “batteryless” ultracapacitor jump starter that should work for decades. It puts out some 400 CCA. Never has to be charged to work unless the jumpee is 100% flat, but can be charged ahead of time and will hold it for many months.

That said, an ultracap-only starter may not meet your specs.
Schumacher does make a hybrid lithium/ultracap 900 CCA jump starter. It may avoid some of the worst problems of battery-only jump starters, and it sure-as-heck should start that powersmoke. It’s about $330-350.

I’ve used their battery maintainers and chargers for decades and found them to be pretty good quality. I’ve used the ultracap starter 4-5 times, usually after sitting unloved for many months, and it’s worked just fine. Bought it 3 years ago.

Ooh, looks like there is an 800A ultracap-only version, but no longer sold by schumacher in the USA. Sold in Europe/UK under “HERTH + BUS” brand .

OK, also sold under John Deere brand in the USA for about $265.