Lipo kit on a budget.....
https://hobbyking.com/en_us/turnigy-nano-tech-1200mah-2s-25-50c-lipo-airsoft-pack.html
https://hobbyking.com/en_us/turnigy-12v-2-3s-basic-balance-charger.html
(Both are in stock & in UK - stuff can be located all over the place UK - EU - Hong Kong etc..)
G&G crane stocks can be a bit slim - 18mm to 20mm max diameter with about 5 inch or 126mm length
You could get some slightly larger size/capacity ones but they may/may not fit so easily....
They might also be out of stock UK & order from EU instead (no biggy but 2 x postage or order all EU)
G&G crane stocks can be a tiny bit smaller but that lipo should fit ok no problem
(you MUST measure your gun to be sure before ordering though)
Charger - cheapo B3 type charger that charges through balance lead - a bit slow but idiot proof
no fancy setting n crap - charges through the small connector or balance lead as its called
needs a psu but if you got and old psu from say a modem/router it "might" fit
or a fancy variable voltage laptop universal psu can be used if you got half a clue
or splice the ends of the lead that comes with it and wire it up
IF YOU KNOW WHAT YOU ARE DOING !!!!!!!!
Budget setup that gets you going cheaply, 2 batteries + charger under £20 inc postage)
(If you get into this stuff then rewire to deans & ditch small tamiya then
get a B6 (genuine model if possible than a clone copy) charger blah blah blah)
They come off charge @ 8.4v - 2 x 4.2v max volts freshly charged btw