Looking for 52v Downtube

So as title says im looking for a 52v downtube battery I want highest ah as possible but my budget is £350 I don't want any dangerous garbage, I would like closest to 20ah as possible but good quality and safe at the same time.

Can anyone suggest any websites or specific battery's please

Thanks in advance

My motor is BBSHD 52v 1000w 28A