If you have them unlocked, Defibs should be a standard part of most of your kits

Two resucitators take up 4 slots, and yes, are cheaper. A set of defibs with no extra batteries revives 4 times, and takes up the same amount of slots. Bring an extra XL battery, and you've increased your total revive capacity to 14 or so.

Generally speaking for most kits, bringing defibrilators should be a non-negotiable part of your loadout if you have them unlocked. You can revive more, stay mobile while charging them, slot them to a quickslot like an inhaler, extra batteries take up the same space as a third inhaler AND revive 10 times the amount for the same slots, and finally, they WILL pay for themselves.

You don't need to bring batteries, but bringing the fibs themselves should be something you start incorporating into all your loadouts when you unlock them.