I'd go for these
https://landlmodels.co.uk/collection...7-6v-120c-brca
good value for money,
Or personally I've just got these, for just a bit more
https://www.pbmracing.co.uk/products...ne-hv-2s-lipo/
The Intelect listed above are 5mm tubes, but you could use adaptors if you felt like.