Spill containment is not required for Valve-Regulated Lead-Acid (VRLA) batteries. These batteries are sometimes referred to as “sealed” or “maintenance free” batteries. In short, there is nothing to spill as the electrolyte is completely absorbed in the micro- porous plate separators or is gelled.
https://docslib.org/doc/2601969/battery-spill-containment-is-not-required-for-vrla-batteries

