Hi, Also purchased similar item.
I found 'FlyHi 300A Peak 8000mAh Portable Car Jump Starter Power Bank(Up to 2.5 L Gas Engine, NOT FOR DIESEL Engine), with Powerful USB Charging Port, Built-in' item which I bought via Amazon (no other choice at time so had to use amazon) & gotta say, this got us out of trouble a few times (you may have to copy and paste into google to find item if reply does not show this as a 'clickable link'). Really easy to use &, due to forgetting to recharge after use, actually had over 3 or 4, uses before recharging. Open bonnet, conect both crocodile clips to corresponding nuts on battery, let power pack/power bank rest on 'engine' & turn ignition key/button...immediately started car as if new battery had been installed. Never go anywhere without it now and have actually had to use recently when temp fell to near freezing and below for almost a week & car had also been parked up for a few days. Truly is a cracking piece of kit an is literally about the size of 1 of todays, what some people call 'mobile phone' but about as wide as a packet of fags!. Also has a torch and ability to recharge mobile phones, although never had need to use either of these functions. Definitely beats carrying around pair of lengthy heavy cables or 12v jump start tool that is about size and weight of a car battery, to begin with!
At the time of purchase it had been knocked to just shy of £30 at £28.99, original price was between £70 - 80.00. If you can grab one of these must have gadgets, get it!