In July I fitted a Yuasa U1R 30Ah CCA330 from Tayna, its now a little cheaper than the £49 I paid. It drops straight in but the terminals are at 45deg so you may need to ease the cables to fit. Its a maintenance free battery. More expensive on Amazon though supplied by Tayna. My Banner lasted 7 years.
https://www.tayna.co.uk/lawnmower-batteries/yuasa/u1r/
