I think the battery situation could be fine. I have a wireless mouse that boasts 3 year battery life. Since a 'dash' would only ever need to switch on and send

I think the battery situation could be fine. I have a wireless mouse that boasts 3 year battery life. Since a 'dash' would only ever need to switch on and send a quick signal when pushed (which for detergent might be 50 times a year?) I imagine it could live for years (say a few hundred pushes) on a single cell.