Guided access

I have a restaurant in São Paulo where I use iPod Touch 5 with costumized app (Aloha Mobile) for tabel waiting. It was all fine until we upgraded to iOS 7. Guded access is a great tool 'cos we were able to lock the app so staff had access only to our app. Baterry life was around 8h. Problem is that Apple, for some crazy reason, dissapiered with the feature "Enable Screen Sleep" in iOS 7 !!! Now our battery life is cut down to 5h!!! Yes, it does dimm the screen down to lat's say 25% after the amount of time you set in "Lock Screen" feature, but that's not the sollution. Not to mention that it means we´ll have to provide at least 25 new iPods to overcome this sudden predicament!!! Any ideas?

Alek