Extra battery is overrated IMO. For maverick Reduced Tool Energy Consumption is more bang for the buck (basically +100% energy rather than +50%, for the main tasks you're gonna spend it on in a Mav - using the cutter and the overcharge), and it's among the easiest mods to engineer yourself. For dominator there are other higher priority mods as well, like ammo, shield, jump, DR... For artemis sure it's good, but by the time you're diving into exobiology, you're likely able to afford to engineer it yourself.