The Goal Zero components are primarily a battery, and an inverter, the rest is bells and whistles, packaging and marketing. You can put your own setup together for a fraction of the cost. An experienced off grid home supplier, like backwoodssolar.com, will be able to help you. Lean on their experience, they have been doing alt energy for 30 years or so, and then buy from them. You will get more for less money, just no fancy box for it all.
Before you contact them, buy a WattMeter, one of those devices you plug into your home outlet, that digitally displays the amount of watts being used by the thing you plug into it. Or do the math, but have a number to give them, "X amount of watts." Then determine how long a fully discharged bike battery takes to re-charge. That's all they need. This is off grid design 101. I will be very surprised if you don't end up with twice the power for half the cost of buying a Goal Zero. Charge the big battery at home to start, solar can always be added later, 100 watt panels with controller less then $100.00 delivered. Or just buy a small generator, quick and dirty, but would work for sure.
For my plane, I had a custom built voltage booster made, so while flying, my plane's 12 VDC system is charging my 52 VDC bike battery at a bit over 2 amps. Solid state, and highly efficient, and that's important because I only wanted to draw about 12 amps out of the plane's system. I just checked their site so I could provide a link, and the 30+ year company has closed it's doors, retired. Some one else can no doubt do something similar, a much better way to go then inverting 12 VDC up, to run a charger, and then converting it back down.