Battery size

[Jeff Barnes]

Can you put any size 12 volt battery in a 1974 bug . Can you over size cranking amps and hurt your car and starter. Speedy are you out there?

[Marc]

The battery box area is designed for a Group 42 battery, and there are few other choices that aren't either too long or too wide to fit in the available space. The 42 is also very low, to allow for plenty of clearance to the rear seat springs - you can use a taller battery if you make sure it wouldn't short out and explode if a passenger sat over it. Modern side-post batteries like you find in GM cars present a flat top surface, but you'd need to change the cables to accomodate one (there exist screw-in adapter posts that'll accept conventional cables, but in my experience they aren't 100% reliable - besides the possibility of there not being enough clearance between them and the pan or seat-support rail).
No harm will be done to anything in the electrical system by fitting a larger-capacity battery.
http://autos.yahoo.com/maintain/repairq ... 030_3.html
http://www.rtpnet.org/~teaa/bcigroup.html