multiple servos locking up

I am using 12 MG996R Metal Gear servos on an Arduino, externally powered by a 7.2v NIMH battery. When I put a load on the servos they sometimes do this thing where they all go in weird directions (maybe to the highest or lowest degree of rotation?) and stay locked there. It doesn’t matter if I reset the Arduino or remove and reattach the battery, the servos stay locked up until I unplug every single servo and then plug them back in one by one. I’ve also tried powering with a 5v 3amp power supply, but had the same issue: https://www.amazon.com/gp/product/B005T … UTF8&psc=1

Question 1:

I’m assuming this is some sort of issue with the servos drawing too much volts or amps? I’m not sure whether I need to get a power source with more amps or more volts.

Question 2:

I’ve heard of powering through series vs. parallel… is this the sort of problem that could be solved by attaching the servos in series? Right now they are in parallel (all of the blacks are connected to the battery ground and reds connected with battery’s red). I’m scared to try series cuz I don’t wanna blow up my servos or battery.

But maybe that’s not the issue at all.

Question 3:

also, not all of the servos bear load at the same time. six of the servos are almost always in motion (and bearing load) while one set of four is in motion (and bearing load) alternating with another set of four which is not in motion while the other set moves.

I was wondering if maybe I should get two (or maybe even three) different power sources, although this seems like it would be a pain with wiring, charging, cost, etc… But if I did, should I divide the set of six that’s always in motion to distribute the current draw?

like I could have three of the constantly moving six with one set of alternatively moving four servos. And I could even split up the alternating set of four servos so that two in motion share a power source with the two in rest? Sorry its hard for me to articulate this all through text. But the most important issue is issue number 1 above.