The value of the sealed packaging outweighs the assumed contents or their condition. People will pay a premium for a sealed item, often if they intend to keep it sealed themselves... so the actual condition of the item inside ends up being irrelevant. Only if they bought a sealed item to open it, then it would be a factor to them... but if you are investing in sealed figures, keeping them sealed would be the better investment. If you are likely to open it up in the future, then remove the batteries if you want - but be aware that most small battery damage is usually reversible. The large batteries (AA or bigger) can leak a lot more acid, damaging plastic and the more delicate electronics if they are in the path of the acid (gravity).