Spare non-spillable lead acid batteries are permitted only in carry-on.
Non-spillable lead acid battery contained within a device can travel in both carry-on and checked luggage.
Non-spillable lead acid batteries:
You can carry a maximum of two spare batteries as carry-on only (the terminals must be protected).
Batteries can overheat and catch fire.
You will be asked to relinquish all dangerous or prohibited items found in your carry-on luggage. If you refuse:
AvSec X-ray bags going onto aircraft to ensure there is nothing dangerous in them.
For more information, see Retrieving your removed items.