With iOS 9 beta 1 coming out this week we have now started to see that a lot of users have reported bad battery life. And yes this is the first beta so bugs are to be expected. 

A few users have stated that if you disable Siri in your settings on iOS 9 that it will increase your devices battery life. So Siri might be the gas guzzler of iOS 9. If you have battery problems and just don’t want to downgrade. You might try disabling Siri. Let us know if this works for you.