It looks like you have to remove the battery to get a better angle.
The problem you have is that the extension you have on steals all the torque you are using on the handle.
The extension,s always twist alittle like the torsionbars in a suspension.
Most of the force you use to turn is being used to twist the extension instead and you only got something like 30-40% of the force down where you need it to be (just made up that number)
Use a shorter extension or put a piece of pipe on the handle to give you more torque
How does the extension look like that you are using?
Does it look like this:
Notice how they are different at the end where you use the ratchet and socket.
The first one is useless the more force you use on it the more it will twist like a torsionbar and then finally snap.
I dont know how many of those o have destroyed untill i found the other one.
The second wont twist so easy, i have never destroyed one that looks like that.