DO NOT pull the injectors just to install new o-rings unless there is strong evidence that one or more is leaking badly. The symptoms of that would be that it wouldn't run or would run extremely poorly.
They are not a normal, "while you're in there" maintenance item and the protocol for pulling them is involved. Removing them is no big deal but the issue is the HP oil system, (and a smaller amount of fuel), emptying into the cylinders and draining the system. Not a fun or easy job even if you know what you're doing.
You tested all 8 glow plugs independently outside of the truck and they were all dead? A little hard to believe but if you say so. If the truck starts ok w no glow plugs in warmer weather, you have good compression and a healthy engine. The batteries draining down rapidly while cranking it over is normal and another sign of good compression. It takes a lot of juice to spin over a 7.3 liter V-8 w 17.5:1 compression ratio.
The factory battery grounds are more than sufficient, just make sure the cables are good and connections not rusty. They already ground to the 800 lb. lump of cast iron under the hood, you are not improving anything by doing it another 1,2 or 3 times.
You do not say what year or how many miles it has but that could allow for some more specific advice.