[Teddy1975]

You can fit a new battery without issues. However, the official instructions include telling the CEM (central electronics module) that you've fitted a new battery so it can adapt the charge pattern to it. You can do that yourself with Vida/Dice or have someone do it for you.

You need a 10mm socket and an extension for your ratchet wrench. A large straight-edged screw driver is recommended to help open two plastic clip retainers.

Procedure is:
Remove top of battery tray
Disconnect the (-) cable at the far end of the battery by loosening the 10mm bolt, you don't need to remove the bolt completely. Yank the connector off, it may spark as you remove the cable and this is normal.
Disconnect the (+) connection at the near end of the battery (that's the one made out of metal)
Follow the red cables down the front of the battery box and unclip the two retainers holding them
The front and sides of the battery box is one piece, remove it by gently prying it from the rear part of the box. You can see where the parts fit together at the top of the box.
Unbolt the battery retainer clip from the bottom of the box
Lift the battery up and out. Do not tilt it more than 25-30 degrees or you risk spilling battery acid
Install new battery in reverse order, finishing with reattaching the (-) cable. Tighten the bolts so they are good and tight, don't overdo it. Use a permanent marker and write the date of installation on top of the battery.

I've left the battery out of my car for several hours while working on it with no negative side-effects after reconnecting the battery, so I wouldn't worry about that.

/Teddy