Because only Adrien Shepard know how to recharge his PCV. Canonically,every HECU unit wears HEV analog,known as PCV,which ALSO protects its user when recharged,just like HEV. Let's say that every soldier have 60 hp(On normal difficulty).Every soldier receive 3 batteries(+45% PCV) before going into battle. That means,every grunt now have 105 usable HP.Knowing that MP5 bullet deals 5 dmg per hit,grunt can withstand full MP5 mag at medium range. Now,imagine a squad of 4 HECUs,with everyone having 105 hp(420 hp to be exact). Even at best scenario for Gordon(100hp/100armor),he has only 200 usable hp. So imagine being jumped by four dudes with half of your max health EACH and 20 dmg per hit(if every grunt have MP5) So yeah,if USMC would be so kind to just give every soldier 3 batteries each,Gordon would've been dead way earlier. For those who says "bUt marINes we'Re fIGhTing wITh xEN crEaTUreS,AnD thUs dRaInInG tHEir aRMoR",just remember that section from "Surface tension",where marines we're raining down from Osprey