I hope you're off by an order of magnitude on that current rating, or it might not deliver the goods when you need it...

He didn’t give a current rating. “mAh” measures energy storage, and 3100mAh is enough to jump a car a couple times.

Jumping a car doesn’t take a lot of energy. But it does take a lot of power (and therefore current). Small Li-ion car jumpers can be surprisingly capable.

I jumped a stranger’s car with my 66.6 Wh battery the other day. DC output 12V/10A. Peak current 2000A. Battery is still ¾+ full. Haven’t tried charging a phone from it though.

I have actually used this thing several times to jump a car. It works great.

Those are great to have. I will say that 3100mAh is pretty low and wouldn't even fully charge most smartphones. 20kmAh batteries can be purchased for less than $100, and 10k-15k mAh for less than $50.

A good idea to have just in case. :)

Someone already mentioned this but I want to clarify that mAh alone is not a full measure of capacity.

OP mentioned his mAh rating in 12 V but you’re comparing it to Ah ratings in 5 V. OP’s battery should be able to charge a full smartphone fine.

Also, most of those 10-20k battery packs won’t be able to jump start your car because they have greater capacity but cannot provide power quickly. There are high capacity battery packs that do jump start but they’re over $100 from the last time I looked.

I purchased a 20,000mAh “jump pack” for $120CAD two years ago to use with my boat. I’ve jump started it with no problems, and this was a Mercruiser 350. I’ve also boosted a car and a truck in -25C weather. They work great, are super portable and only weigh 2-3lbs.

Caveat - unlike a standard battery booster pack (lead acid), lithium battery does not take kindly to freezing temps, so it is useless to keep it in the car over winter. I wouldn’t expect to be able to start anything in the middle of winter up here unless it was kept indoors at room temp.

Spoiler, it works.

I use a lithium booster battery pack for an old car I use, and have used the battery pack to jump-start my car multiple times on a freezing-cold day (sub 10f) while trying to locate a store with a new car-battery in stock.

Amp-hour ratings only should be adjusted for voltage if a DC-DC converter is used. If the jump starter uses a cheaper linear regulator, the amp-hour ratings remain the same. (The excess energy is discarded as heat.)

I had a cheap one 5 years ago that was able to jump start a car. The instructions said to leave it connected to the battery for 30 seconds before trying to start it, so I guess it's more a portable battery charger than a jump starter. For sure if you disconnected the 12V battery and only connected this it would not work.

Since you are probably not talking about kilometeramperehours, might want to fix the unit to just Ah.

Battery packs are usually marketed with their capacity in milliamp-hours. I thought the 15-20k mAh made it pretty clear that we were taking about a 15000-20000 mAh battery pack.

They are, but SI prefixes are always combined, not used together. 15k mAh is just wrong. The correct way to write it is 15Ah.

I believe the k in “15k” is a suffix and thus not beholden to the rules of SI prefixes. In this case it is used as shorthand for “thousand”, and this usage is prevalent even in countries where SI units are not commonly used.

Insisting on changing 15k mAh to 15 Ah is the same as insisting on changing 15000 mAh to 15 Ah - which seems to be a matter of personal preference more than anything.

Mind you that's 3100mAh at 12V. That's roughly 7400mAh at 5V (USB voltage).

That is assuming a DC-DC converter. 3100 mAh is 3100 mAh regardless of voltage if the charging functionality uses a cheaper/simpler linear regulator.

Indeed! That's a good point. If it uses a linear regulator, I guess the thing would produce quite a bit of heat when drawing power from the USB ports - the extra energy would just be converted into heat.

Is possible battery damage or malfunction due to the heat in a car a concern?