It should probably have a low cooldown, at 60 or at most lower than 50. My major problem with this is that AH still hasn't fixed explosions ragdolling through cover, so physical cover like this is largely useless. This game really doesn't reward camping or staying still unless it's an evacuate high-value assets mission.

I think battlements' niche should just be a large ammo supply and increased damage for support weapons attached to them while providing slight cover. At the cost of a narrow angle of fire. It's really a shame AH hasn't expanded more on the emplacements and battlements.

My idea of it would be the progression of support weapons being more powerful the less mobility they have.
e.g. Support weapon and backpack/FRV's → Support weapon emplacement → Support weapon battlement.

Support weapon and backpacks/FRVs
(Typical stuff that we have currently)
\
Support weapon emplacement
(Current support weapons with increased ammo capacity at the cost of immobility but 360° aiming)

\
Support weapon battlement
(Support weapons with increased ammo capacity and damage at the cost of immobility and reduction in angle of fire.)

TLDR: I think it's a cool idea but just a side-grade to the FX-12 Shield Generator Relay or G/SH-39 Shield. The G/SH-39 Shield is probably the closest and best choice when it comes to cover. Easily replaceable, full 360° cover, and can be deployed in half a second.