You will have a lot of trouble shipping a battery.
IATA (International Air Transport Association) have banned the shipping of most Lithium-Ion battery by plane. This is due to the fact that the batteries can be susceptible to random ignition if the conditions are not correct and the battery is not packaged correctly.
Batteries that are contained within electronics ARE allowed. Up to a capacity of 100Wh (IIRC)
Batteries which are just a battery, but have protection circuits and no exposed contacts providing full voltage ARE allowed up to a certain capacity (100w/h IIRC) - such as power banks
Batteries which are just a battery, without the proper casing, with exposed contacts, without protection circuits are called CELLS and ARE NOT ALLOWED except for very very very specific cases and circumstances.
These apply to both passengers and Cargo.
If you are travelling as a passenger, All LI.ION batteries must be held in the cabin, and not allowed to go into the hold.
P.S. I often use this as an excuse to keep my hand luggage on me and not be forced to send to hold "My hand luggage contains lithium-ion batteries that exceed the allowed amount for hold luggage according to the IATA rules, therefore I must take the hand luggage on board the plane"
https://www.iata.org/en/programs/cargo/d...batteries/
RE Original Problem of laptop replacement battery.
Possible Solutiuons:
1. Find someone who is flying in. Check battery specs and ensure its safe to fly with it in hand luggage.
2. Find a way to ship the laptop back to the UK, declaring that it contains LI-ION batteries (will cost more) then have battery swapped in the UK and shipped back here.
3. Find a local repair shop, you will probably need to visit many, get quotes, let them handle everything.
Sorry I didn't spot this earlier. I was in Mainland Spain last week and drove back - so would have avoided any IATA rules. Sorry