So im about to detail the engine bay on my 2004 ford ranger XLT with a 3.0, and im wondering if i need an obd2 memory saver for when i take out the battery.

 

No
If you check the codes after everything is hooked back up you will see P1000, this just means battery was disconnected for longer than 5min
It also means engine computer(PCM) will now run emissions testing and memory testing over the next 2 or 3 drive cycles
It will clear P1000 on its own after that if all systems pass the tests, if not it will set other codes for why a system didn't pass the test

1 drive cycle is when engine is heated up above 160degF for longer than 10min and then cooled down below 120degF

 

thank you very much