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I have a Juno Jumper I use that good for up to 3.5L V6 vehicles (though I have jumped a 4.6L V8 once with it), flashlight, micro usb charge, USB, +/- cables. Nifty little jumper.
I noticed someone getting jumped today in a parking lot and now this thread... I decided to buy this powerhouse. Great ratings and one of the ratings is from a AAA road side assistance guy that said he jumped 9 cars in one day with a single charge. The LCD is important to me.
If you're looking at lithium-ion jump starters, get the largest one you can afford as most of them have over-inflated specs. They're good for cars that won't start due to lights being left on overnight. I've used many of these jump starters and they'll do great most of the time until you encounter an aging battery with a severe voltage drop. I usually have to bring out the larger lead acid jump starters since they're more capable in terms of delivering heavy current. There is a limitation to how much current those little lithium packs can safely deliver without severely degrading the cells.
With that being said, I used to have the NOCO GB40 until water got into my trunk and destroyed it. It was a decent unit but there were times it just didn't have enough power to jump start a car unless it was fully charged. I replaced it with the Schumacher SL1. The selling point was the use of LiFePO4 battery chemistry. Longer life span, MUCH better thermal stability...important if your trunk gets HOT, and typically higher current discharge rate (more amps the better!).
If it wasn't for my small trunk space, I would have gone back to the Jump-N-Carry JNC660. But of course it doesn't fit in my pocket.
Got an "Everstart" at Walmart for only about $40. It's about the size and heft of a red brick and seems to be built relatively well.
These portable boosters are important to carry along if you have a hybrid, because if the 12v battery is just a bit low it's not that the engine will "crank" more slowly--nope, instead, the system won't boot at all. And you will have no warning beforehand.
Haven't had to charge it up since I bought it in October, but I would think every six months or so sounds about right.