Nearly a year ago, the battery on my 4-yr old 307SW died, I took it into
one of the National Chain type of Replacement Exhaust, Tyres & Battery
Centres for a new Battery. Over an hour later, they admitted defeat as
they couldn't work out how to get the old battery out - it is stuck
behind quite a few other bits & pieces in the Engine compartment!!

John

It is covered by a plastic trim which you remove by taking off both
leads and pull the cover out. There may be another cardboard type
piece which will just pull out. Then undo the fixing bolt at the
bottom and remove the battery.  BUT. . . .
It is VERY important to make sure the BSI is "asleep" before you
disconnect the leads. So make sure the ignition is off and the keys
out for AT LEAST 3 minutes. Preferably 5 minutes. This gives the ECU's
and BSI a chance to shut down properly and save all the settings. Then
when the battery is back in place you need to do a gentle "wake-up" by
switching on the headlights (leave the window open to do this. Don't
open the door first). Then open the door and start the engine. The
only the thing you may need to do is initialise the driver's window.
If it goes up in inch stages, get it right to the top, then hold the
switch up for a few seconds. Also the radio may need the stations to
be retuned.
This all applies to any multiplexed car.

However I have never hadt a duff battery smelling of burning rubber.
Why do you think it is the battery? Did it actually start the engine
that morning? Check the belt for cracks on the ribs and also the
pulleys and tensioners for wear and contamination. It has an automatic
adjuster so won't go out of tension. At least until it is well worn
and will probably break then!