Okay, If you are feeling brave and have "some" diagnostic skills....(or willing to learn some new things)... it seems most people with old Baileys have opted for the Lipo option.
They take a little more caring for than lead acids.
The following are "Slow Boat from China" prices (ebay) £16
I use one of these £26 (I couldn't find the exact model I use) This one is marked as a C60... not sure I believe that but as long as its at least a C20, that would give you 150 cranking Amps £3.... XT60 solder one of these to your battery leads
You will need to cut the charging wire