Am I cooking my battery?

[Chexi]

Ever since I bought my 2000 SAN last year, when the motor is running at moderate to higher rpms (other than idling basically), my in-dash voltmeter would go above 14 volts. Over the weekend, it was reading 15.5 volts. I measured at the battery while running the motor with a portable tester and also got 15.5 volts. When I turned the motor off, the battery read 14.5 volts. Am I cooking my battery? Is my alternator or some sensor bad? I don't know much about this part of the 12v world, but I see short lines and long lines on my gauge, and long lines are usually there for a reason.

[AirTool]

Before I give any electrical advice...

It seams very strange to me that your battery would read 14.5 volts with the engine off. It seems chemically impossible to me.

Are you "gauging" (pun intended) all this with the dash gauge? ...do you have a digital multimeter you can clip on it?

[Chexi]

I used a digital multimeter. It surprised me too.

[DanielC]

The in dash volt meter is pretty inaccurate. Check the voltage, at the battery. Not on the cables that clamp on the battery posts, but on the center of the actual post on the battery.

The voltage should be 13.5 to 14.5 volts. This is for a conventional lead acid with wet plate battery. Other types of batteries have a slightly different voltage.

First thing, if the voltage is above 14.5, check the water level in the battery. Add some if needed. Go to a grocery store, and get distilled water, and use that.

The next thing to do would be to clean the battery terminals. Then check the voltage again.

If the voltage is still high, ask a dealer about it. It could be the voltage regulator inside the alternator is a little out of spec, and replacing the alternator is possibly a way to fix the problem.
If the voltage is not that much above 14.5, keep an eye on the water level in the battery. If you need to constantly add water to the battery, you may still need to replace the alternator.

[Chexi]

Thanks Daniel. My battery is a 1 year old AGM battery (It's the Die Hard Platinum big one built to military spec... rebadged Odyssey). My buddy took the reading, so he might not have taken it from the battery posts.

I do have a 100 amp alternator upgrade that I have been meaning to install, so I might just finally bite the bullet and do it.

[AirTool]

I used a digital multimeter. It surprised me too.

That is strange....a chemist would tell you it can't be higher than 12.6 unless you have 7 cells....not even a chemist from East Texas.

And like DanielC pointed out in different words, when you overcharge them, the battery won't overcharge....it just boils out the water.

Maybe you can find or borrow a cheap inductive (magnetic) ammeter and hold it up to the back of the alternator to see how many amps are coming out. If the regulator is stuck fulll....it is full amps to the battery. (But I haven't seen one of those in years.)

[east tx skier]

That is strange....a chemist would tell you it can't be higher than 12.6 unless you have 7 cells....not even a chemist from East Texas.

I resemble that remark, except I'm not from east Texas. I'm from Houston. I'm not a chemist either, I suppose.

[AirTool]

I resemble that remark, except I'm not from east Texas. I'm from Houston. I'm not a chemist either, I suppose.

I remembered one of you guys was transplanted...maybe two. (one from Louisiana or at least out of Texas? ...I remember a discussion about a stuck jeep in the river bed.)

People from South Texas (and Houston it seems) always make fun of people from East Texas. So the question is: who do people from East Texas make fun of?

[ckdollar]

Thanks Daniel. My battery is a 1 year old AGM battery (It's the Die Hard Platinum big one built to military spec... rebadged Odyssey). My buddy took the reading, so he might not have taken it from the battery posts.

I do have a 100 amp alternator upgrade that I have been meaning to install, so I might just finally bite the bullet and do it.

Guys at Buxton warned me against an alternator upgrade on my 99, claiming they have had them fry the electronics in the boat. I don't know anything about it, but that's what they said!

[Chexi]

Buxton told me the same thing. However, I know that a lot of people have made the upgrade, including the techs at Tyler Ski N Sport, and I have never heard any of them talk of this danger. Buxton may have had it happen once, but it could simply have been a defective new alternator.

The folks at Buxton may say they have the best mechanics and disparage the folks at Ski N Sport (they did to me anyway), but the folks at Ski N Sport used to work for Southwest Correct Craft (when it existed) for many years and are really the ultimate experts in the area on Nautiques. As proof (to me anyway), Ski N Sport fixed my distributor issue when Buxton could not.

[ckdollar]

My gauge typically only reads about 12.5 volts charging when we are underway. I have not checked it with a meter, but I have checked the level of the battery a few times after a right, and it is always 100%, so maybe the gauges are just not very accurate.

[Beach-TJ]

It is normal for a motor to put out up to 14.4 V when at operation rpms (ie, moderate to high rpms). So seeing just over 14 volts on the meter is nothing to worry about. But 15.5 volts is. If your motor is charging at 15.5 volts, then it will be putting your battery into a Gassing state, which can cause it to explode.
A battery will hold a surface charge, often above it's 'real' charge level for several hours after charging. If your system is charging at 15.5 volts, it would be expected that your battery would show around 14.5 volts for several hours after the motor is shut off. The 'proper' way to check your battery's level would be to shut the boat down, and turn off your battery switch, then allow the boat to sit for a good 12 hrs. Then check the voltage level of your battery, the surface charge will have had enough time to discharge naturally, and you should see something around 12.6 volts. If so, your battery is still healthy.
I run the same batteries in my boat, if I think about it when I get home I will check the resting volage of one of them, but I believe I remember it being right around 12.6 volts.

[Chexi]

Thank you!

[Beach-TJ]

Just checked my Die Hard Platinum, which happens to be one year old. It has been sitting since Sunday, the last time I used the boat and is showing 12.81 volts on my hand held volt meter. I thought I remembered these batteries resting voltage was a bit high. The batteries switch has been off since Sunday, so it has had plenty of time to discharge the surface charge. But the gauges on the dash are only showing 12.4 volts, and the one in the perfect pass shows 12.2 volts.
My boat normally shows around 13 to 13.2 volts when the motor is idling, and up around 13.8 to sometimes as high as 14.4 volts while under way. This is by both the analog (looking) volt gauge on the dash as well as the digital volt meter built into the RPM gauge.

[TX-Foilhead]

I talked to Scott about this the other night, but thought I would post it for others. I was resetting the gains on my amp a few weeks ago as per JL specs with the multimeter. After I finished and buttoned everything up I tested a stereo battery just for grins to see what all the gain setting had drawn from the batteries. I got a reading of 19 volts, I figured my cheap multimeter had probably started to crap out after a few years. Not wanting to completely give up on it I changed the battery and tried again and got 12.4 at the same battery. So if you get a very odd reading check the battery in your meter. Now I have to go reset the gains again, but at least I know they aren't too high till I get around to it.