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Old 16-11-2006, 08:17   #1
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Battery voltage too high????

After being connected to shore power for two days and being charged by a Xantrex TrueCharge 20, my batteries had the following voltage reading:

Windlass = 18.25
Start = 17.95
House = 13.97 (we have been using lights, refrig, etc.

All batts are AGM and I have the TrueCharge set on:
AGM - Bulk/Absorption - Warm (temp).

The batts are not hot and I'm not experiencing any problem (yet???).

Is this normal?


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Old 16-11-2006, 09:28   #2
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No, it is not normal yet possible under some conditions. First, are you actually measuring the voltage DIRECTLY across the battery terminals of each battery using a DVM?

What is the status indication of the charge lights on the Trucharge?

Does the charger go to float voltage when you remove all loads from the house battery leaving an elevated (around 14V) voltage on the other batteries that have had no load?

If the AGM batteries are not warm and have full charge as well as capacity then they will not charge accept current at elevated voltages yet it is not desirable to allow this conditon to exist without monitoring the current into each battery to verify that it is not charge accepting sufficient current so as to gas the battery. Some good quality AGM and gel-cell batteries will not gas at elevated voltage once they are cool and are at both full charge as well as full capacity.

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Old 16-11-2006, 12:12   #3
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No, this is NOT normal under any circumstances. I'd suspect the meter first, i.e., you need to verify that the meter is reading correctly.

Second, you need to measure the voltage AT THE BATTERY TERMINALS. With the charger off, and after a reasonable resting period, you should not measure more than 13.8 volts or so. Once you've bled off the "float charge", the voltage should be more like 12.7-12.8 with AGMs.

If somewhere on your boat -- any circuit -- you are in fact reading higher voltage than the voltage at the battery terminals with the battery charger off, then SOMETHING IS WRONG. Exception: if you are using a diode-based battery isolator AND if the charger is set up for it, you could read .5 to 1 volt higher or so than at the battery terminals (the diodes cause a voltage drop).

It's hard to imagine that a Xantrex charger would produce voltages as high as you are reading, even in the "equalization" mode (normally, about 15-16V). Solar panels, unregulated, could do this.

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Old 16-11-2006, 12:43   #4
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"you need to verify that the meter is reading correctly."

Yep, that was it. I had not noticed that it was giving me a low battery display. Changed the 9v battery in the meter and everything is reading like it should.

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