It's useful to have a battery because it means we can pretty much be self sufficient in the summer. But yes, we have been told it will need replacing in 10 years. It has a 10 year guarantee, so should be good until then. I guess we'll see how things are at the time. Replacing it isn't compulsory, obviously. We did have the roof re-felted about 15 years ago, so hopefully that will last well. But yes, if we end up needing the roof replaced, we might regret the whole thing!