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  #1  
Old 11-08-2009
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Battery Voltage Issue

My boat has two Grp 27 batteries that I think were new in '07. Since buying the boat in May the voltages usually are close to the same when checking with the voltmeter built into the boat system. (Using a multimeter indicates a higher voltage than the built in gauge). I am plugged into shorepower and have a charger on 24/7. A few weeks ago I checked the battery fluid using one of the cheap floating ball type testers and the batteries tested good, all fluid brought up to full.

The last two times at the boat I've noticed the #1 battery is showing about 11.5 volts while #2 is about 12.5 volts. I didn't have a multimeter with me so I wasn't able to check the batteries.

My concern is the change. Any ideas on why?

Thanks
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Old 11-08-2009
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Just a thought...

Wire resistance will affect to some degree the measured voltage to the two different areas, as will terminal corrosion or any poor connection.

You also may have a cell in your one low voltage battery going bad dragging it down..

Are they two separate banks or do you have them parallelled...if so I would disconnect it from the good battery so it doesn't drag that one down as well and have it load tested .

Edit: FWIW I quit keeping my boat pluged in 24/7 I go plug it in once every couple weeks...My battries have stayed hot and in good condition for over 2 years now.
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Last edited by Stillraining; 11-08-2009 at 04:04 PM.
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Old 11-09-2009
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11.5 VDC is almost completely discharged. How is the charger connected to the batteries? How old are the two batteries? Chances are likely that your charger is only charging one bank, and not the other.
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Old 11-09-2009
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Quote:
Originally Posted by sailingdog View Post
11.5 VDC is almost completely discharged. How is the charger connected to the batteries? How old are the two batteries? Chances are likely that your charger is only charging one bank, and not the other.
AFAIK the batteries were new in '07. They are set up as two banks with a switch "Off All 1 2"

I'm not sure of how the charger is connected to the batteries -- what difference does/would it make?
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Old 11-09-2009
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If you are measuring the batteries at their posts while the charger is on you will be measuring the voltage the charger is putting out. If this is the case you either have a bad charger or a bad connection from the charger to the batteries. While the charger is on measure the voltage at the connection closest to the charger to see if it is different. If it is the problem is in a connection although I don't think this is likely. If the charger output is low when on or the same as the low battery measures you are probably measuring the battery voltage. In this case turn off the ac and check the fuse in the charger. Best to unplug shorepower to be safe. When you turn the charger off the batteries if ok should measure close to 13+ volts, slowly dropping to 12.9 or less over time. If after some hours one measures close to 12 volts then it is very probably a bad battery. If a battery has a shorted cell there will be continuity between the posts. A good battery will never have continuity between posts. If this is the case it needs replacing - a shorted battery will usually blow the fuse internal to the charger.
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Old 11-09-2009
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I just saw your newest post. It does make a difference. If the charger is routed through the "Off,1.2.All" switch the position of the switch determines which battery will be charging. If it is in "both" then it doesn't apply. But if the charge is routed through the switch and it is in "1 or 2 " positions then that could be the problem.
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OK, thanks for the info.

The boat is 150 miles away and we just got our first snow so it'll be a couple of days before I go back to the boat, but at least I've got some ideas on what to look at / check.

Thanks.
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This is the reason a lot of boats have an ACR or Echocharger type device installed...so that a single output charger can charge both batteries whenever it is operating.
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Old 11-10-2009
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Most definitely find out where the battery charger is attached to the batteries. Also look at the battery charger and see if it has only one output or two outputs.
- - The output of the battery charger should not be through the battery switch such that you need to have it in "All" to get the charger to charge both batteries. Assuming the boat is out of the water for the winter, the battery switch should be in the "Off" position to keep any accidental short circuit from starting a fire or depleting the battery. A trickle charger will keep the batteries up for the winter - or - if the batteries are small, remove them and take them home where they can be kept warm during the winter.
- If the battery charger has only one output then use a battery combiner to allow the charger to charge both batteries and also protect an internally shorted/bad cell battery from dragging down the other battery.
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Old 11-11-2009
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Something else to consider, leaving your batteries on constant charge will kill them, although most chargers claim that they will shut off when voltage reaches a preset level, THEY DO NOT. A 1 amp "Float Charge" will kill a battery and balloon it in less than a year from overcharging. Previous owner had a 1.amp trickle charge solar panel on-board (which I still have an use) an the boat sat for a year an a half before I bought it.
The former owner was shocked as the 2 brand new 8D gels he installed a year an a half earlier looked like party balloons, amazing that they did not explode, an I did check to see that it had all been connected properly an the solar controller was set for gel batteries.
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