The experience of Portable jump starter battery?

Has anyone had any experience using portable car jump starter power bank’s as an external battery for their location sound equipment?
I’m looking for a budget external battery for my basic boom and lav kit and have come across these. It seems to have a good capacity, output’s 12v, fairly light weight and be very affordable compared to NP1 solutions. Or am I missing something?

Here is some example of the product:

http://ift.tt/2tPukUh

http://ift.tt/2sl67BA

http://ift.tt/2tOT66J

Regards

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The experience of Portable jump starter battery?