Originally Posted by Paul_Rochdale
This may or may not help you but using a small car battery is often done here in the UK. You don't say what bike you have but I once fitted a battery intended for a Reliant Robin three-wheeler to my BMW R100/7. The closeness of the top tubes of the rear subframe meant that the top edges of the battery had to be relieved by 2mm each side (using a Surform tool). Not as scary as it sounds. The bike happily like this for years but it was a tight fit.
Car batteries are a lot cheaper and with longer warranties. It's seems logical to use them.
The bike is R60/7. The size of the car battery is 187 mm x 127 mm x 227 mm. I'll go to garage to see will the size be an issue. Manchester - Real is playing tonight
so I must be quick.