In the standard MINI (not the S type) the batter is under the hood and it's a simple plastic case top to remove first. I assume therefore that you're talking about the S type.
The battery on the MINI S is under the rear seat space. Lift up the rear seat and you'll find the battery right there. However, the battery in the 2002-2006 MINI COOPER S is, indeed, behind the seats under the floor by the rear hatch. You'll have to go in through the front door, fold the seats down, and contort your body and damage your spine to lift the floor cover, loosen the battery terminals, and heave the battery out.
I will assume you mean "Does a Mini Cooper have a battery?" Yes, they do.
2005 Mini Cooper replace car battery. Alternative to MINI part
$166.45 at Mini Cooper Dealership, but you can buy it at Western Auto for $145.99.
You can change the battery in your Mini Cooper by releasing the hood lock located on the bottom portion of the dashboard. The key to unlock the battery cover should be on the side of the battery cover.
Batteries Plus
No
Use your key in the door.
Purchase a simple battery charger like a Battery Tender, or a Ctek. Follow instructions.
To change the battery in the Mini Cooper keyless remote, it is necessary to first open the device. This can be done by removing the key chain and gently prying the seam at the opening end apart. Now the battery is accessible for easy replacement.
It will delete the pre-programmed radio stations.
a good light weight factory type battery would be the mini cooper battery or the CSL m3 battery
Not necessary. No problems will be encountered when changing the battery.