How to insert a RYOBI HP 36V 6.0Ah or 9.0Ah battery into an older RYOBI Lawnmower

Good to see there’s a larger 36V capacity and with HP technology but I’m really disappointed just how obscenely large this battery is and why the new 4Ah is just as big as the 5Ah. Hopefully there’s actually a weight difference. Seems like re-using moulds or something - just cheap.

Could you also please tell me why the difference was with the previously-new BPL3650D2 5Ah battery was technology-wise? I noticed it had a newer sticker/colour scheme and 1x dimple on top instead of the previous 2x. I initially assumed this battery must’ve been HP technology because the 18V ONE+ HP batteries came out at the same time.

Can this battery be purchased individually?

Too easy!

"RYOBI’s new, longer runtime HP 6.0Ah & HP 9.0Ah Batteries come with a battery door extension which creates a weatherproof seal around the battery for older 36V 40cm & 46cm Lawnmower’s manufactured before December 2019. Please note – if you have a 36V Lawnmower manufactured before December 2019 you do not need the battery door extension to fully seal the battery door – simply slide the battery in place and feel the HP difference!"
This text make no sense

Ive got the Ryobi 36V pressure washer system and also own the newer 6.0Ah batteries for my 36v Lawnmower but sadly the 6.0ah battery will not fit in the pressure washer unit and i cant not purchase a 5.0ah batter seperate on its own. (wasn to insert 2 batteries into the pressure washer for longer run time). Will the 5.0ah batteries ever be sold separate or not?