Batteries are among the heaviest loose objects on a yacht. In a knockdown or a hard slam, a battery that isn't held down becomes a projectile with live terminals on top. Securing them is cheap, which is why surveyors grade a loose battery hard.
What the standard asks
ABYC E-10 covers battery installations. In our words: each battery must not move more than one inch in any direction when a pull of twice its weight is applied, for a minute each way, up, fore and aft, and side to side. Positive terminals must be insulated so a dropped tool can't short them. Boxes aren't required, but flooded batteries need full containment for acid. The fixings for a box or tray must sit outside it.
Steve D'Antonio, writing in Cruising World, thinks the one inch is too generous. He calls the thin nylon strap common on production boats inadequate for a seagoing battery and prefers complete immobilisation with a clamp or heavy straps with stainless buckles. For lithium, Panbo reports that ABYC E-13 asks for no visible movement at all.
How a surveyor checks it
Grip each battery and try to move it. Look at what holds it: a strap screwed into a plastic tray, a buckle rusted half through, a clamp with no bolt. D'Antonio notes most self-tapping screws would fail the static load test. Then the terminals: is the positive covered, and how close is it to metal that could touch it if the battery moved. Under flooded batteries, look for a box or tray that would hold spilt acid.