Jumper packs can be very convenient, put you pay a large price for that well marketed convenience.
First, the standard 12 or 18 A/h AGM batteries inside are Asian AGM batteries. These AGM batteries do not excel in the low self discharge area as do other higher quality AGM batteries. They are barely better than regular flooded batteries which can self discharge at 15% per month
So they are made in Asia, shipped over here, and sit on a shelf in some warehouse or in some retail establishment for who knows how long before somebody buys it.
The battery at the date of purchase could already have lost half of its capacity. Never to return, and yet the purchaser is completely ignorant of this.
Now the other features of a jumper pack, like the lights. Pretty much worthless.
The wall wart charger for them will take days to replenish the battery from 50%, and if you look at Universal battery's recommendation for recharging in cyclic service, they require upto 14.8v, and way more than the usual 800 Mah or less provided by the provided charger., which might only output 13.7, so the provided charger is not even well matched for the battery.
The Air compressor will say run it for no more than 5 minutes, then let it cool for 30 minutes before restarting it. Running one of these for 5 minutes will take a Standard size 235/75/15 Van tire from 32 to 38 Lbs. The compressor will still make noise after it overheats at the 6.5 minute mark , but the tire will be slowly deflating while it depletes the battery. It will not work properly one it has cooled down either after an overheat. The piston cup is burnt and can no longer make a seal with the cylinder wall, so all it does is make noise and deplete the battery.
If one wants such a cheap miserable unreliable compressor, goto harbor freight and buy their yellow 5$ version. It will be just as 'robust' as the ones integrated into these Sleek jumper packs.
The Inverters in some models are too large for the battery inside it. a 18 A/h battery cannot provide 400 watts for very long at all. Also if one were to put a voltmeter on the output under a significant load, instead of 115 volts AC, one might see less than 90, Which might damage the device attempted to be powered.
If one is looking to use these as a power source, to use instead of the vehicle battery, well, it is pretty fool hearty to use the Backup battery for primary duties, in my opinion.
If one really wants a jumper pack, and they do come in handy, I am not arguing that, then get one without the bells and whistles, Just a jumper pack with a handle and alligator clips. Perhaps a useless light, but no more than that.
Or better yet just carry jumper cables and an 18 A/h AGM battery
http://www.atbatt.com/sealed-lead-acid-batteries/b/universal/m/universal-ub12180.asp
But for double that price, one can get a group 24 marine battery containing 85 amp hours capacity, and never worry about needing a jumper pack.
I found that when I did have a jumper pack, It was most convenient to lend it to others to jumpstart their vehicles, rather than driving over to jump them. Of course then it was compromised for when/If I needed it.
They might be a good emergency item, A 'feel good' back up, but don't rely on them to take the place of a real battery, or a real inverter, or a real air compressor. If you continuously run the battery down to where it cannot power the device being powered, do not expect that the battery within will last long at all.
The batteries can be replaced, if one has the skills and possibly the tools( like a long reach torx t-20 screwdriver), to do so. They do not want customers replacing the battery in our disposable world, they want them to buy another one so they make it difficult as possible to actually do the responsible thing.
Usually one can buy the same rating of each of those devices, of higher quality, for cheaper than the all in one jobbers in their sleek plastic exteriors.
So buyer beware of sleek marketing , sleek packaging, with cheap as can be internals manufactured at Slave wages in the third world.
