This is sounding less and less like AdEva and more and more like X-COM: BIG ALIENS EDITION.
To create an alternative AE setting, you need to answer just a few questions before you can begin.
First; how were the EVA series created? You need the biological basis, and a means to produce it. This is best reflected in the science of the time. Given the 60s, I'd say something along the lines of Lysenkovication and artificial fertilisation; bombarding the captive Adam with intense gamma radiation until it buds off a Core, taking the Core before it begins to grow as an Angel, imprinting a human structure onto it by injecting it with a human fetus, and then leaving it in a strictly controlled artificial environment for the years it takes to grow to full size, accelerating the process by taking it, snap-freezing it in liquid nitrogen, and then defrosting it to cause a stress response. The Societ process is similar, but uses Lysenkovication more directly, snap-freezing it until it is clinically dead, causing fractures along the core while it is energistically dead and won't explode, then reactivating it by colossal radiation bombardment, so that a number of unpleasantly deformed and weak EVA base creatures are grown, each with its own Core shard. This also makes them much weaker AT-wise, but far less prone to Berserking.
The second question is hwo are you going to power them? There'd be worse batteries, and very large, to the point that being battery-powered entails carrying an apartment-building-sized box with you with a short cable leading to it. You also need to have a nuclear power facility and specially-designed cabling anywhere you intend to deploy, unless you seed the battlefield with shitloads of these batteries in advance.