I did a "test" some time ago and here's what I found out (about my Kobo's battery life):
WiFi was off in all 3 "tests" and I only read ePubs.
1.
sleep: 15 minutes
power off: never
firmware 1.9.17
ca. battery life: 2700 page turns in 12 days
2.
sleep: manually every time when putting the Kobo away
power off: 1 hour
firmware 1.9.16
ca. battery life: 4200 page turns in 24 days
3.
sleep: 5 minutes
power off: 10 minutes
firmware 1.9.17
ca. battery life: 4350 page turns in 15 days
So for me, powering off the Kobo and rebooting it when needed (was about 3 times a day) resulted in a far longer battery life (more page turns).
Don't know about firmware 2.1.1 yet (of course, not enough time to test
).