As above, you do NOT remove the seat itself.
You remove two bolts on the floor at the front of the seat and it then hinges backwards to give access to the battery.
Here's a how-to with video:
www.mytreg.com
You remove two bolts on the floor at the front of the seat and it then hinges backwards to give access to the battery.
Here's a how-to with video:

Changing the T1, T2, T3, T4 AND T5 battery, including...
NOTE: There is a well meaning video on Youtube where the guy takes out the entire seat on a T1. You do NOT remove the seat on a T1 or a T2 - it hinges backwards. But you do remove the seat on a T3! HOWEVER, as of 20 October 2014, go and look at post #72 before you take the T3 seat out as it...