It doesn't say how many watt-hours it is, but I'm guessing it's lithium, 14.8 volt configuration (four cells in series to produce enough voltage to start a car), so 177 watt-hours? That's a surprising capacity for the price and size, compared to laptop and drill batteries. It's 2-3 times the capacity of most laptops. I wonder if they are calculating mAh wrong. When you put cells in parallel mAh add but volts stay the same. When you put cells in a series, volts add but mAh stay the same. They likely need a series-parallel arrangement to get enough voltage to start a vehicle and to get 12,000mAh capacity.
Here's the biggest hobby lithium pack I could find (I didn't look very hard):
5000mAh 4S 14.8V 25C LiPo Battery from Hobby Express
It's about half the size of this device, so there's either two massive batteries like that inside and they use super cheap cells (cheaper than I can find from any reputable source while leave some margin for profit on the product), or there are smaller batteries inside and they are overstating the capacity. Sixteen 3000mAh 18650 cells would fit, but that wouldn't leave any room for electronics to charge and balance the cells. Higher capacity cells at a cheap enough price point are probably overstating their capacity. For example:
Amazon.com: 12Pcs 18650 3.7V 5000mAH Rechargeable Lithium Battery Yellow: Electronics Check out the reviews on those. Notice how many reviews have the title "Five Stars" then have a line of text that's really general.
400A means a 33C discharge rate for a 12Ah pack, so it's a reasonable claim but a bit hard on the batteries. It should be OK since starting doesn't usually last long. But if they are overstating the capacity, there's no way it could deliver 400A.
I don't doubt it can start a car/truck once or twice, but I'm skeptical that it meets the specs they claim. In my opinion it's not good enough to rely on if you need it to jumpstart your truck in the middle of nowhere. In a few years it will have significantly less than its original capacity because lithium batteries deteriorate with heat, age, if they are stored fully charged, and if they are not cycled occasionally. All of those things would be a problem for this device.
Most larger jumpstart packs use surprisingly small 12V lead acid batteries. I considered buying a jump starter, but then I realized I already have a 7Ah lead acid battery, identical to the replacement for some jumpstart packs, so I'll just keep that in my truck and use it with my jumper cables if needed. It's hard to believe such small batteries can start cars and trucks, but I guess they get some help from the starter battery if it's not totally dead.
If I was going to spend that much money I would put it towards a dual battery system that would be useful to power a lot more than just cell phones.
Note: I have not used this product. I'd like to take one apart and see what's inside, but they have a 20% restocking fee on returns. If anyone buys one and doesn't mind opening it up, I'd like to see how it's made!
