Hi Mate..
I have a Traxide dual battery system in my 2014 D4.
I also do a bit of motorcycle touring.
For power needs while camping, I use a Power bank + starter below:
20000mAh CAR Battery Charger Jump Starter 1000A 12V 24V ATV Boat Truck Tractor | eBay
Touch wood I have not yet had a reason to use it to start my D4 or motorcycles... but charges Laptops and iphone/ipad etc.
Cheers
Bala

