Mrs Green has been pootling around the inter-webby learning about experimental battery storage technology.
On our journey we discovered, via Great Green Gadgets, a clever little clock that is powered by a battery that uses ordinary tap water.
According to Hammacher Schlemmer this little time-keeper can be powered for up to 12 weeks before needing a re-fill. Sadly, it seems that they are no longer selling it. Taking time-out perhaps?