I always like having a big battery in my cars. If you ever run into carby troubles you can easily flatten a small standard battery trying to start it, or if your alternator or wiring isn't fantastic then it can give you a bit of extra juice before you go flat. It's also handy for the times you build an engine and crank it without ignition to get oil through it.
I measured up the battery tray and room available in my KE30, went down to Autobarn and looked at what they had on the shelf.
I went from a standard MF43 battery (238Wx138Dx186H) with 360CCA to a SuperCharge MF52 (237Wx171Dx182H) with 650CCA. Fits perfectly with a new 7" battery clamp.
I started a new page on the wiki for batteries:
http://www.rollaclub..._Series/Battery
(inb4 someone criticises me for adding 4.5kg of sprung weight to the front of my car)