How easy is it for wet cell batteries to spill?

[chabrenas]

This is related to my post about chlorine, really. Many years ago I sailed pretty hard in boats which used wet (flooded) cell lead-acid batteries without even thinking about the potential problems. How far do you have to tip a battery before there is a risk of spillage? Is it really not a problem for a traditional displacement yacht, even in heavy weather?

Clearly, an Ocean 60 or 70 (a Vendée Globe or Volvo Ocean Race canting keel monohull) has to use SLA/VRLA batteries, either straight Gel or AGM - being heeled over 110° and even completely inverted are part of the conditions for which they are designed.

A follow-up question is: how general is the use of Gel or AGM batteries among traditional displacement-hull racing and cruising sailboats? Does anyone have a good feel for this?