I'd like to put together or buy an off the shelf power pack, power station, or whatever it's called to provide auxillary power (for running a 40L Waeco fridge/freezer for a day or maybe two, and providing periodic/intermittent power to a 1,000W inverter), to top up the starter batteries (24V). Lithium batteries should be good for longer term storage and it'd be handy to have the whole package as compact as possible (think my last attempt with AGM batteries weighed in at around 35kg/80lbs - both large and heavy), but with lithium batteries I'm guessing I can't simply hook them up to my current shunt box (designed for lead acid technology batteries) so I need to incorporate some kind of 24V lithium battery charger/controller and find some lithium batteries which are happy to be wired in series. I'm based in Europe/Norway/UK - any suggestions?