ba.com states that boots and skis packed separately may each incur a separate extra bag charge:
We will accept skis and snowboards of all dimensions provided they are packed correctly.
Preparing skis and snowboards for travel:
• skis and snowboards must be packed in a recognised ski or snowboard bag
• if you are travelling with skis and ski boots you should pack them in one of the following ways:
- pack your skis and ski boots separately*
- pack your ski boots within your checked baggage
* Each bag that exceeds your free checked baggage allowance will incur an extra bag fee.