Long story but.........my friend died a few weeks ago and I've been tasked with selling on his Hopper Urban folding electric bike. I have a friend who wants to buy it but.........it hasnt been used for a few years and, try as we might, we cant find the battery! It was bought from Tesco years ago and so I'm a bit lost as to which bettery to buy to replace the missing one. It wasnt one of the "Frog" type - but I remember it was black and quite a slim rectangular shape that slid into the casing above the rear wheel. Fortunately I managed to find the key. Any experts out there have any idea which spec battery I should buy, and where to get it from.