Yes indeed, there seem to be more and more complaints about bad batteries. Either the new devices somehow got a huge fat batch of terrible batteries, or there is indeed something horrible going on in the firmware.
I'm glad you won't have any problem exchanging your device!
I think the factory settings are 15 minutes to sleep, and "never" to off-mode. If you want to be 100% sure, you could always do a factory reset for your final test