Battery losing some Charge(95 Chevy 1500)

Okay here's the problem. The needle is fluctuating between 9 and 14, closer to nine really. It doesn't do it right off just after it has ran for a while. The alternator is new and the battery was taken out of another truck, same model and worked fine in it. Once i put it in mine, I thought it would do the trick but that was not the case. Ironically, I put my battery in the other truck and it worked fine with a reading at 14Volts. I need another belt tensioner cause I have noise coming from it but I'm not sure it that's causing the problem.

Okay here's the problem. The needle is fluctuating between 9 and 14, closer to nine really. It doesn't do it right off just after it has ran for a while. The alternator is new and the battery was taken out of another truck, same model and worked fine in it. Once i put it in mine, I thought it would do the trick but that was not the case. Ironically, I put my battery in the other truck and it worked fine with a reading at 14Volts. I need another belt tensioner cause I have noise coming from it but I'm not sure it that's causing the problem.

so you think the alternator is good I guess? Do you have a voltmeter to check the alt output? If your alternator is putting out 13.0 volts are better it should be ok. The only real way to test a battery is to have it load tested.

The belt tensioner could cause an alternator to fluctuate if it causes the belt to slip. I would start by checking the voltage the alternator is putting out at the alternating using an analog voltmeter, you can use a digital voltmeter if it has an analog display. I would not use a normal digital voltmeter because they update the display at slower intervals and it would be harder to check for fluctuation. Place the positive lead on the alternator wire (thick wire) on back of the alternator and place the negative lead on the alternator housing. If the needle fluctuates on the voltmeter then you know it is fluctuating and not a problem in the vehicles voltage gauge. Check for loose connections while you are at it

I forgot to mention that my positive cable has a wire that goes to an amp spliced into it. It's not hooked up to anything so I doubt it will have any effect on the battery. I'll troubleshoot it still and see what I can come up with.

check for loose wires at the starter motor, loose battery or corroded battery cables at the battery and check for loose or bad main grounds

Check all your grounds. If the power wire has been spliced into this could be a prob. I would rerun a new power wire as well as new amp wire. They need to run seperately from one another. The amp will really drain your system if not. Check the amp ground as well. It should be clean and paint free, tight also. If not look into that.

Sorry guys, it has been a while since i last posted a thread on this topic. Been really...really busy with other things. Anyway, I have some time now to re-diagnose the problem i'm having. I have replaced the battery cables with new ones and the battery meter is still fluctuating. So what i have done measured the voltage across the battery while at idle and it's putting out 14 volts. Next i shited the truck into drive with the emergency brake on and measured the voltage across the battery again and it dropped to 12.5 volts. My question is, do u think the instrument panel itself is bad or the alternator is not putting out enough or maybe nothings wrong with the alternator at all. When i purchased the alternor some time back, i'm not sure of the amp output of it. I'm not sure if it's a 100amp alternator....etc...etc...etc.

Just determined that my alternator puts out 105 amps and the battery is brand new as well.