The dumbell is behind the rear drivers wheel, under the bumper, 13mm spanners from memory (4 bolts) to take of the dumbell and the mounting brackets all in one- CAUTION- get the grey matter out of the way, its reet heavy when your under the car, if it falls on you you'll loose 50 IQ points forever.
The battery is in the cabinet behind the drivers seat - easier access with the roof folded down, open the cabinet, remove the interior battery cover (mine has a handle) and then remove the metal strap that goes over the battery (knurled nut on mine then wriggle off).Make sure the live terminal cover stays on the battery, if you dont want to wrestle around in there just disconnect the battery (you may loose your radio code) get rid of the silly plastic under tray and fit an acoustic matt under the battery, I used scrap ends from work but dynomat or similar would do. personally I'd go for 2 densities as it will act as a better spring (at least 1/2" of material)- the whole concept. Shuffle the foam under the battery and use a small camping bungee cord to hold the battery under spring tension.
If you like it it's probably worth removing the battery and gluing the matt in place forever.
It's throwing it down so I'll do pictures if it ever cheers up. It really is easy. I've now gone a bit mad elswhere and installed thin acoustic matt between various squeaky body parts- 2 annoying squeaks left but otherwise a complete transformation