We are not allowed to send batteries in the post but you can buy one easily from your local car accessory shop. You require a 12 Volt 30Ah Battery (originally a 28Ah) with dimensions of 180mm Long x 125mm wide x 170mm high and it fits the BMW motorcycle Boxer Twins Models R80 or R100. Ensure your battery terminals are covered if you dont want your car to catch fire and fit a Battery Isolator Part No 1153. Conventional Wet Lead Acid fair better if you are using a electro mechanical regulator as they tend to overvoltage the battery and Gel batteries do not like this at all!!