Thanks to hackers, the words "portable console" and "removable battery" used to spell "nightmare" for Sony. The battery of the PSP famously offered hackers an easy back door into the console that until then required hard-to-find exploits in games. It's no wonder the PSP Go was a closed system. So what about its younger brother, the PS Vita?
Apparently much easier to get into, it seems. As seen in 4Gamer's literal breakdown of the newest version of the handheld console, it appears that the battery can be easily accessed simply by removing the back cover.
Upon closer examination of the safety manual of the new PS Vita, you can find a generous step by step on how to get the battery out of the machine. It's literally as easy as unscrewing 7 screws, popping off the back cover, and unhooking the battery. (From the looks of it, there isn't even a security sticker)
This can be done on the original Vita as well it seems. Note, however, that doing this serves no purpose other than to completely void the Vita's warranty. Sony actually included this information as part of instructions on disposing of your Vita.
Back before the PSP's firmware security was cracked wide open, hackers discovered that the removable battery had its own software that could be hacked and enable them to install their own independently made games and software onto the console. That's a backdoor method that Sony has probably checked during development of the Vita, so it's highly unlikely it'll be possible this time around.
At the end of the day, if you really want to get to the Vita's battery, it's possible, but really kind of pointless. While it could be useful knowledge for when your Vita's rechargeable battery dies and you want to replace it, it doesn't look like Vita batteries are currently on the market, so you're better off asking Sony to do it for you, rather than give them a reason to say "no" when you want them to repair or replace your Vita if something else goes wrong. The batteries are recyclable, so it's nice to see Sony being environmentally aware at least.