Did you buy a battery for a bike available from alienbikes.co.uk? If so, is the battery you bought one of the bulkier versions like this?

You should be able to strap it to a regular bike rack. If you want the proprietary metal rods and support system that attach to the bike much like a bike rack, you may need to contact the UK distributor directly to make an inquiry about purchasing them. The email point of contact is: jim@alienocean.co.uk. However, the latter option doesn't really give you a functioning bike rack.

If the battery is one of the generic LIFEPO4 in am aluminum case, you should be able to use about any rack.