When I am driving 2000 S-10 my battery gauge fluctuates.

Make sure the battery and battery cables are good. Check your charging system.

In a conventional system the tank sensor provides a variable ground path for the gauge which is fed by a stable regulated voltage from the instrument regulator. Sometimes the regulator will fail and cause a fluctuating voltage supply depending on engine speed, whether the lights are on or off and suchlike. Mostly such fluctuations, if they seem random, are caused by a less-than-perfect connection somewhere, mostly the fuel tank ground connection. Newer systems use a computer to drive the instruments but excellent connections are equally important..

Adjust the blet tension or if automatic tensioner replace the belt and check the tensioner pulley.

Hi,first of all I would get the battery and alternater checked to make shore they are bothe performing properly,I know you have replaced the battery but sometimes even new items can be forty,and with the fluctuation it maybe the maff sencer,the best thing is to have a diagnostic don to find the couse.
best of luck,PH.

fuel filter,air filter,could be TPS sensor,crankshaft sensor.weak fuel pump.

Check that the idle speed is not too low in drive . Should be around 900 rpm in neutral and the idle speed is adjuste in drive to no less than 750 rpm. IT takes rpm for the alternator to charge the battery so if you have 11 volts then the car is runnung off the battery and not the alternator. It needs 13.5 volts to charge a battery and most regultors are set at 14 vvolt to 15.5 volts. If the vehicle is runnung from the battery as I stated then items like blinkers and stop light operation will show as fluctuations on the gauge. Have the system check . Make sure the drive belt to the aklternator is correctly adjusted as a slipping belt will also cause a problem.

The first thing you need to know is what the alternator output is when this starts happening.
It could be a faulty connection in the wiring harness, or a bad ground connection, or a failing alternator.

The oil pressure guage will fluctuate with engine RPM. At idle it should be approximately 20 lbs./sq.in, at high revs about 50-60 lbs./sq.in. Hope this helps any concerns you may have. Good luck!

DIAL IN CAB COULD BE AT FAULT, NEED TO GET ANOTHER DAIL GUAGE AND CONNECT TO SENDER, IF SAME COULD BE SENDER, IF STILL THE SAME, PRESSURE VALVE IN BLOCK STICKING DUE TO DIRT OR U/S, OR AT WORSE !!! ENGINE WORN, THIS WILL BE CONSTANT IN MOST CASES, FAULT IN GUAGES ARE NORM INTERMITANT.
LOTUS

Hi, Did you notice the motor actually reving higher when the tachometer was reading a higher rpm.. If it was it could be your transmission slipping.. Set your cruise control and listen to your motor while the tachometer starts moving erratically.. Good Luck