What does it mean when my battery gage goes from the middle to low all the time Auto zone told me my battery and alternator r fine

You mean your volt gauge. Turn your key to on with the lights off and see what the volt gauge reads. If it reads what what you are refering to "low" as then that's fine. That will be around 12 volts which is normal battery voltage. The mid range reading is when the altenator is working and shoud be close to 14-15. A little higher or lower is alright. If your saying that it is dropping out I would say that your altenator is slowly failing. You can try to clean the wiring connections, but I would bank on it going soon. Remember if the gauges drops to battery voltage and doesn't come back up you will only have a limited amount of time before the battery drains and the engine dies.

As long as the pointer is somewhere in between the two hash marks on the guage you should be ok

To verify the actual voltage to confirm that you gauge is correct read the voltage across your battery with the engine off and when it's running (altenator working) with a multimeter. I will stick to my first comment. In my experiences it is almost always the altenator that causes fluctuations with the volt gauge, second is loose/damaged wires. If the gauge goes high (rare) or low and stays there then it's a gauge/cluster issue.

The regulator controls how much voltage the alternator puts out. If it is dropping the regulator is going out. Which means you need an alternator. Have it checked again with everything on. High beams, wipers, radio, turn signal and see if it will drop out.

I still don't know what's going on with mine. 2003 ford expedition. The gauges all drop to nothing. Gas..battery...oil...speed...ect ... Radio shuts off windows won't work. Any ideas? Recently had a new key ignition pit in as well. Seems like that's when the issue started? I'm not sure if its a coins coinsadince or not.

My 2007 Toyota Tundra battery symbol is on and battery gauge reading low at 12 volts? Would it be the alternator going bad.

What does L and H mean on the battery reader on the odometer ?

2003 Ford ex. My key cylinder was not put in right and u always had to push it in when u started it or your gauges wouldn't work gas speed voltage ect.. if that aint it maybe look into ignition switch