Point being according to RM guidelines it sounds like you were within them for UK deliveries unless you maybe didn't meet their packaging guidelines:
Electronic devices sent with lithium batteries
(including mobile phones, digital cameras, etc) where the battery is not connected to the device.
Packaging guidelines: The maximum number of lithium batteries allowed in each parcel is the minimum number required to power the device plus two spares. For lithium ion/polymer batteries the Watt-hour rating must not exceed 20Wh per cell or 100Wh per battery. For lithium metal/alloy batteries the lithium content must not be more than 1g per cell or 2g per battery. The maximum net quantity of cells or batteries is 5kg per parcel. Each cell and battery must be of a type proven to meet the requirements of each test in the UN Manual of Tests and Criteria, Part III, section 38.3. Cells or batteries that are defective or damaged are forbidden. Cells and batteries must be packed in inner packagings that completely enclose the cell or battery and protect them from short circuit. The equipment sent with cells or batteries must be packed in strong rigid packaging and must be secured against movement within the outer packaging and packed to prevent accidental activation. Must be presented at the counter. Sender’s name and address must be visible on the parcel.
Kick up enough of a fuss and get to the right people and I'm sure you'll probably get money back.
