Is the storage space on common property or does the space form part of your lot?
Would the power point use power that is paid for by the OC, or would you be responsible for it?
If the space forms part of your lot, query whether you have to ask permission, but if it connected in a way that you weren’t paying for the power, then I would say perhaps they are within their rights.
If it were being connected in a way such that you paid for the power, I don’t see what the problem is, you could apply their logic to power points within your apartment…
However – if they have already permitted another owner to do it, find out what the arrangements were, and if yours are the same you have grounds for saying that they are being unreasonable (or the other owner should remove theirs).