surfergirltg

I purchased a new battery for my 2005 v6 mustang yesterday They tested the new battery before leaving the store .Took the old one out and put the new battery in .On the way home I noticed that the battery gauge is reading high and today when I started my car it is reading high again the gauge is all the way to the top .What is causing the high gauge reading and how do I to I fix it ?

Z28KLR

Possibly bad voltage regulator? I would check battery voltage across the posts with the engine running, typical acceptable reading would be 13.4 to 14.2 V. If it is significantly outside of that range, obviously higher in your situation, then it's overcharging for some reason and will cook your new battery in a short amount of time.

Not an auto-electric expert, but my first guess again is bad regulator (internal to the alternator, which means you'd be installing a new one of those). Could also be something simple like a ground strap or something somewhere disconnected or making poor contact.

surfergirltg

I should have mentioned I live in Pa. and right now for the last 6 days the temp. has been 15 degrees and below.I didn't look at the battery gauge when the old battery was in to see if it was a high reading then.My old battery was a reconditioned battery was in the vehicle for 6 years or longer.I figured The cold weather and not driving vehicle everyday during the winter months is what killed the battery.After putting the new battery when driving home is when I noticed the battery gauge reading was high.When I got home I left the car running in order to check to see if it was the alternator I removed the one cable from the battery while the car stayed running the car didn't shut off so I think the alternator is ok.Could it be possible that with the freezing temp.outside the gauge could be stuck or frozen ?

Z28KLR

Possible, yes. Unlikely though. As far as disconnecting the battery while it's running, try not to do that in the future. It's an old trick that is ok for old cars, but on modern computer controlled cars it can be a bad idea.

Technically anyway, the alternators only job is to charge the battery. The battery itself is what supplies all necessary current to power the car. Your test showed that the alternator is providing enough current and voltage to keep the engine running, but because of your gauge reading what needs to be figure out is if it is providing too much. Hence my original recommendation of getting a voltage reading across the battery terminals (with them both hooked up this time, lol) and engine running.

tw1234

Not all new batteries have 100% charge. If you have a battery charger put it on the new battery for a couple of hours. Then remove and start the vehicle and see if the gauge steadies at a lower reading. Most gauges when you turn the vehicle off drop to zero so that would be a good indicator as to whether the gauge is stuck. As mentioned in post 4, a voltage check should be done at the battery running and not running to verify alternator functioning properly.

surfergirltg

I am going to get a voltage reading as you suggested.What do you think would cause it to be providing too much current and voltage? I am a little curious as to what can happen to a newer car if you disconnect the battery while running ? Thank you for your help.

surfergirltg

Thanks for the info.

surfergirltg

Just wanted to let you know I took my car back to where I bought my battery.They tested my car with their diagnostics computer ,The mechanic said there is nothing wrong with my car except the gears that are on the battery gauge one or more must have broken off which is causing the high reading on the new battery and he said not to worry about.Unless I want to have my whole dash tore apart to replace the gauge or gears which I am not about to let any garage to tear apart the dash to fix something so minor and then once the dash is put back together end up having major electrical problems.I don't trust most garages to begin with letting them tear apart my dash.

imp

Sorry, but your statement about alternators' purpose is blatantly wrong. The battery serves only two purposes: provide power to start the engine, and provide power to maintain the keep-alive memories in the various modules. Once the engine starts, the alternator supplies ALL the power to run the vehicle, while replacing the energy lost from the battery due to starting the engine.

Your understanding of basic electric theory is not being doubted. Please understand, go back to the basics of Electric Theory, and look closely at how the Battery and Alternator are wired: They are connected IN PARALLEL, they are both voltage sources, they are both capable of supplying energy to the vehicle, the Alternator output voltage is ALWAYS maintained at a level slightly higher than battery voltage, which means after the engine starts, NO CURRENT leaves the battery; it's always the other way around.