This is not recommendable. Just lets assume you swap out your battery with a 16 volt one. Now all your actuators that are attached to Battery voltage will draw a higher current. Which means you increase the stress on these parts. This can lead to shorter durability on these components. Also the drivers in the PCM (electronic control module that controls all engine and transmission functions will be stressed higher and might eventually fail. I guess that these considerations have priority over having a couple watts more.//content.invisioncic.com/y282845/emoticons/naughty.gif.94359f346c0f1259df8038d60b41863e.gif
This would imply that you also change your alternator so that cranks out more then 16 volts to make sure that your battery will be charged all the time.
If one really wants to go that way then the only correct way to do this is to run a dual voltage system were you add a second alternator that only connects to a dedicated 16 volt amp set up.
Robert