I had a SOTA beams pole - Collapsed it was rather too long to fit into the rucksack - so I used it strapped to the outside. Not ideal - Someone then suggested lifesabreeze.co.uk and I found a 13ft or 16ft (I think) one which collapsed to less than 2ft and fits into my rucksack. I cut the last section off as its too delicate. I use a SOTA beams linked dipole with it and have had absolutely NO problems getting QSOs with it on the hill, including the USA!.
Like you I struggled a little with batteries at the start. I got and used for quite a while 12v, 2amp SLAB batteries. I got a couple of these batteries Security measure (I can’t do a proper link but they are 2amp 12v LiPO at 18 euro, incuding charger) from Ireland later on . They took a week or two to arrive though.
There’s some good info on this thread in reply to a similiar question I asked when I started SOTA Which of these batteries? (please) and I managed to go with a couple of the suggestions but as you now note UK lipo and/or li-0n are harder to get now
David.