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View Full Version : What voltage should battery read?


skilew
05-23-2006, 07:42 PM
What voltage should my battery read at idle and what voltage should it read while running above idle. I sometimes get an audible alarm when the boat idles for a few minutes. When the boat is running I only read about 13 volts.

I took the battery to Autozone and had them check it out and they said it was ok. I also took my alternator to a local rebuild shop and again no problem found.

Any suggestions.

prostar205
05-23-2006, 10:32 PM
when you say running, do you mean at idle or under way 1,500 rpm and more?

At idle, 13V is just fine.

skilew
05-24-2006, 01:43 AM
I mean above 1,500 rpms.

88 PS190
05-24-2006, 02:35 AM
what else are you doing? radio on? navigation lights?

If you drain the boat's battery sitting idling using power to other things its possible that the system will decide to give you the low batt buzzer.

Can only speculate as to that being the main cause, but if the batter load tests fine, and the alternator tests fine I doubt there is anything "wrong"

wesgardner
05-24-2006, 10:22 AM
Yep - 13.6 +/- when running, somewhere around 12 at rest...BTW - panel gauges are NOT accurate...

JimN
05-24-2006, 10:46 AM
Each cell should be ~2.4V for a new, fully charged battery and with 6 cells, you should have ~13.4V at rest. When the motor is running, you're not reading the battery's voltage, you're reading the alternator's voltage. At high RPM, the alternator should be putting out ~14.4V (that's the general design voltage for accessories- look at amplifier power rating specs) and if you see less, you're OK if it's not less than about 13V. Check the voltage with a digital multi-meter if you have suspicions about the accuracy of the gauge.

If the battery terminals are loose or corroded, you'll see lower voltage and the same thing happens if the ground connections on the motor or fuse block or terminal strip in the dash (if there is one) isn't clean and tight. The gauge grounds through the terminal strip or fuse block, then that ground goes to the block in most cases. At a minimum, there are two ground points between the gauges and the battery. All voltages need to be referenced to the battery terminals.

If the battery has been totally dead, you won't see the same voltage as a new, pristine battery.

tommcat
05-24-2006, 11:09 AM
Each cell should be ~2.4V for a new, fully charged battery and with 6 cells, you should have ~13.4V at rest. actually it is 2.1 volts per cell for a total of 12.6 volts on a good, resting(no load) battery.

JimN
05-24-2006, 11:24 AM
OK, I just looked at some notes and if we want to get tweaky, a battery that's 100% charged will show 12.66V, open circuit. :D

Charging voltage should be about 13.4V- 14.6V. If it's significantly outside of this range, more testing is needed.

This sounds like a voltage drop test would be in order.

88 PS190
05-24-2006, 01:11 PM
He still hasn't clarified if the 13 is from a dash guage or a multimeter across the battery terminal.

Be nice if you dropped by to chat skilew!!!

Lots of good things to think about in here.

tommcat
05-24-2006, 01:27 PM
OK, I just looked at some notes and if we want to get tweaky, a battery that's 100% charged will show 12.66V, open circuit. :D

Charging voltage should be about 13.4V- 14.6V. If it's significantly outside of this range, more testing is needed.

This sounds like a voltage drop test would be in order.You are correct but most peoples meter wont read that far out so i didnt bother mentioning it :headbang:

skilew
05-25-2006, 09:38 AM
I am reading the voltages from the gauge.

I look at it again and actually the voltages are lower than I thought. It actually is around 11 volts at idle and no more than 13 volts above 1500 rpms.

wesgardner
05-25-2006, 10:08 AM
Just remember, panel gauges are NOT accurate, check all your connections as JimN suggests (including grounds) particularly if it's on older boat - things can "look" good but not be electrically sound...I've gone to all-soldered connections on my battery wiring to insure there is as much as posibble getting to the stater, seems to have made a fair amount of difference.

Wes
05-30-2006, 12:17 PM
I had my alternator rebuilt this winter, installed a new battery and the volt meter is reading 7 volts. I am taking the boat to the electrical shop this morning and will let everyone know what they find. It seems to be a common problem with our 'mature' boats.

Wes

Wes
05-30-2006, 06:06 PM
Turned out to be a faulty wire between the ignition switch and the volt meter.