Hi there, Andy. We appreciate your feedback on Nest Protect (battery). We're sorry to hear about your issue with its battery life. The device requires Energizer Ultimate Lithium AA (L91) batteries. We don’t recommend using rechargeable or alkaline batteries. If you do, they will quickly drain and will need to be replaced soon after installing them. Using other types of batteries than the ones recommended by Nest will be detrimental to the smoke and CO alarm operation. Don’t mix and match batteries, and don’t place new batteries in with old batteries.
If help is still needed, feel free to visit us at the following support link for further assistance: https://support.google.com/googlenest/gethelp