Where to buy 12v charge regulator to charge arduino battery?

My arduino runs off a 9AH 12v gel cell battery ( bit of overkill but it's good for prototyping at the mo)

Anyone know where I can buy a 12v charge regulator to run from mains 240v?

Then I can leave it plugged it but if I want to move it around or there's a power cut it will stay switched on

You can something like this

12V Battery Charger