Photos is currently part of the Google+ app, so if you disable Google+, you won't be able to use Photos.
To reduce Google+'s battery usage, open Google+, tap Menu>Settings>[your account]>Location sharing, and turn it off. You may want to turn Auto-Backup off as well, because if it's on and you have it set to backup any time, it might use more battery as it checks frequently for any changes to the photos on your device or in the cloud.