Yeah I was looking into this https://www.componentshop.co.uk/11-1v-1300mah-15c-continuous-discharge-lipo-airsoft-battery-123mm-long.html This may fit, gonna buy the rebel one first though and see if that will fit.
Also, I was looking into https://www.tactical-clothing.co.uk/product/titan-power-version-70-111v-3000mah-li-ion-nunchuck-battery-deans-connection-215479?gad_source=1&gclid=CjwKCAiAjp-7BhBZEiwAmh9rBSmkLsUkjVLFGT7nph_OsxCxO9vQgBMoswzHiIAd-nRmGKSDdCJ7pBoCPSMQAvD_BwE titan batteries.
Does anyone know why they are so expensive?!