Did my onboard charger cook my battery??

[Flyingmike]

I have two batteries on my boat. #1 is a marine starting battery and #2 is a group 27 deep cycle. I showed up to the boat last night and noticed that my #1 only had 10.5 volts, I was like that can't be correct because I have a Guest Marine batterie charger installed. I turned on a few lights and sure enough volts dropped to 4 volts, "yep that battery is dead!!" But why wasn't the charger charging it? A quick examination with my hand held volt/amp meter said the charger was putting out 10amps at 10.5 volts on #1 and 12.8 volts at 1 amp on #2. I felt the side of #1 and it was extremely warm, and #2 was room temp. Also #1 fluid level is good and was bubbling and continued to bubble even after I disconnected it.

I disconected the charger from #1.

So the question is did my charger malfunction on #1 & kill my battery? Or did my battery short a cell and my battery charger is just trying to recover it?

I don't want to kill another battery if it's a bad charger, and if it is a bad charger is there any hope for saving this battery?

[Dave Neptune]

Mike, the battery probably shorted out or a plate separated, thus the 10.5 on the charger and virtually nil with a draw. Probably not the charger as the other seems fine as well as the charge rate.

If "dual" charger check the ofending bank by putting the dead batteries charge line on the good one and observe the charge and voltage.

Dave Neptune

[Flyingmike]

That was my thought initially, that's why I disconnected the charger and then tested the voltage on it. I know chargers will adjust charge voltage based on battery condition but I thought the minimum voltage it would put out is 12v but I guess it's possible for it to start at 10.5 and go up from there. I guess I could disconnect the other side and see what it puts out.

[ndutton]

Mike, you're under a common misconception of battery charging circuits that the regulator (alternator or shore power charger) varies the voltage based on the battery's needs.

In terms of the simplest system, the regulator strives to maintain a constant voltage by varying the output amperage to keep up with the battery's needs, usually somewhere between 13.8 and 14.4 volts. Sometimes the battery needs more than the charger can produce, it doesn't keep up and a voltage drop results. Note that the charger isn't dropping the voltage, it just can't keep up.

With the introduction of "smart" charging profiles there are small variations to the output voltage depending on which charging phase you're in, bulk, absorption or float but in the purest sense battery need affects amperage, not voltage.

Don't feel alone. The concept of variable amperage is lost on many, many boat owners.

For your reading pleasure:
http://www.madelectrical.com/electri...witworks.shtml

I think you have a dead and damaged battery, the odd voltage readings due to the batt sucking the life out of the charger.

[Al Schober]

Agree that #1 seems to be dead. And don't blame the charger - seems it was doing the best it could. 10 amps was all it had to give, and #1 battery only provided 10.5 v resistance at that current. And it sounds like that 100 watts was all going into heat.
The new battery chargers are very good - I'm particularly impressed with a unit bought recently made by C-Tek - their model Multi US 7002. I bought this to try and restore a dead pair of Group 31s. They had been discharged to 4 volts, and my old charger wouldn't do a thing. This new charger brought them back to 70% capacity.

[Flyingmike]

Originally Posted by ndutton

Mike, you're under a common misconception of battery charging circuits that the regulator (alternator or shore power charger) varies the voltage based on the battery's needs.

In terms of the simplest system, the regulator strives to maintain a constant voltage by varying the output amperage to keep up with the battery's needs, usually somewhere between 13.8 and 14.4 volts. Sometimes the battery needs more than the charger can produce, it doesn't keep up and a voltage drop results. Note that the charger isn't dropping the voltage, it just can't keep up.

With the introduction of "smart" charging profiles there are small variations to the output voltage depending on which charging phase you're in, bulk, absorption or float but in the purest sense battery need affects amperage, not voltage.

Don't feel alone. The concept of variable amperage is lost on many, many boat owners.

For your reading pleasure:
http://www.madelectrical.com/electri...witworks.shtml

I think you have a dead and damaged battery, the odd voltage readings due to the batt sucking the life out of the charger.

I agree that battery could be dead and if it wasn't before I am sure it is now. I just want away to test the charger before I hook another battery to it. I put my volt meter on the charge leads after I disconnected it from the battery and it was only putting out 10.5 volts. Shouldn't it be higher than 12, more like 14?

[ndutton]

I wouldn't necessarily trust open circuit voltage as a diagnostic tool for the charger. It needs a battery connected so the charger can determine state of charge and adjust its output amperage accordingly.

A charger by itself is not a power supply.

As an example, I just measured the voltage of my known-good Schumacher shop battery charger. Open circuit measured 0.0V, connected to an AGM battery (11.36 volts at rest) it rose to 13.28 volts. This shows a couple of things:

• The open circuit vs. connected voltages as I described
• The shop charger has a maximum output of 6 amps. Pretty clearly the low state of charge of the AGM is demanding more and the charger can't keep up as described in my previous post.

[Flyingmike]

Originally Posted by ndutton

I wouldn't necessarily trust open circuit voltage as a diagnostic tool for the charger. It needs a battery connected so the charger can determine state of charge and adjust its output amperage accordingly.

A charger by itself is not a power supply.

As an example, I just measured the voltage of my known-good Schumacher shop battery charger. Open circuit measured 0.0V, connected to an AGM battery (11.36 volts at rest) it rose to 13.28 volts. This shows a couple of things:

• The open circuit vs. connected voltages as I described
• The shop charger has a maximum output of 6 amps. Pretty clearly the low state of charge of the AGM is demanding more and the charger can't keep up as described in my previous post.

Ok, I have a spare group 24 from my RV that I can put in there. Well see how it goes.

[ndutton]

Please take three voltage measurements and report back:

• You already have the open circuit voltage of the charger, something like 10.5V
• Measure the battery before connection. This will give us a baseline and rough indication of battery state of charge.
• Measure the battery after connection and charger on.

[Flyingmike]

So I believe the charger is good. I pulled the old battery out and the date on it is from 2008. So pretty sure this battery ran its life. However I'm still not any closer to solving the problem. I just replaced my group 24 batteries on my RV with a pair of Trojan T-105's (btw those batteries are amazing). So the group 24's are only 2 years old and don't want to hold a charge and so I took them down to Auto Zone to be tested, they said 1 was good and 1 was bad. I put the good one on the Boat and let it charge for the past 3 weeks. Come back to it and charger is putting out 13.5 volts when I show up but when I put a load on the battery it dies a quick death. So I thought maybe the guy at auto zone told me the wrong one was dead, so I swapped them again and let it charge. Put a load on and it dies. So it could be I have 3 dead batteries or it could be bad wires, next plan of attack is to swap the wires with the good battery.

[romantic comedy]

I had a couple of L-16 6 volts charged by a Statpower True charge 20 amp smart charger. It also charged a group 24 12v battery for starting. The charger has two outputs and can also act as a power source.

One day I go to the boat and the L-16s are practically dry. They were boiling away. I checked the battery level often, so this happened suddenly. The batts were not more then 2 years old. They are now 120 pound weights hanging out in the back yard.

I replaced the charger with an exact duplicate. I replaced the L-16s with T-105s. I keep a close eye on them too.

I have heard that when using 12 volts often at the dock can cause the charger to over charge the batts. I am not sure about this, but I am leary that it could happen. If I did use much battery power I would change the setting to "constant 13.5" similar to the inverter in my camper.

The T-105s have had a few times, in the past 6 years, where they needed a lot of water.

The group 24 is 14 years old and is finally shot, but never had any over charging issues.

I am just relating this for what it may be worth. I am not sure what happened.

[Flyingmike]

Originally Posted by romantic comedy

I had a couple of L-16 6 volts charged by a Statpower True charge 20 amp smart charger. It also charged a group 24 12v battery for starting. The charger has two outputs and can also act as a power source.

One day I go to the boat and the L-16s are practically dry. They were boiling away. I checked the battery level often, so this happened suddenly. The batts were not more then 2 years old. They are now 120 pound weights hanging out in the back yard.

I replaced the charger with an exact duplicate. I replaced the L-16s with T-105s. I keep a close eye on them too.

I have heard that when using 12 volts often at the dock can cause the charger to over charge the batts. I am not sure about this, but I am leary that it could happen. If I did use much battery power I would change the setting to "constant 13.5" similar to the inverter in my camper.

The T-105s have had a few times, in the past 6 years, where they needed a lot of water.

The group 24 is 14 years old and is finally shot, but never had any over charging issues.

I am just relating this for what it may be worth. I am not sure what happened.

Battery Supply is paying $.25 a pound for recycling old batteries, that's $30 worth of paper weights sitting in your back yard.

I bought the RV back in Oct and when I showed up the po had the house batteries on a charger so my guess is they had been sitting in the RV for several months and therefor had drained down to nothing hence why they are dead after only 2 years old. I had started to look at putting T105's on the boat for next summer but with buying the RV and needing to replace the batteries right away I decided to give the T105's a shot on the RV first. I can't say enough good things!!! And the boat will def be getting a set of T105's.
A quick example camping trip over Thanksgiving week. First night it was raining so the family spent the whole night in the RV watching movies and playing games. I run the TV for several hours off the inverter and had the lights on in the coach the whole time also the heater kicked on and off every few minutes all night long because it was 35 degrees out side. All in all I figured I was averaging 7-8amps an hour for about 12 hours out of those batteries and expected to see them around 50% (12.1v) by morning. Woke up and tested the batteries and they were at 75% (12.5v). I was very pleasantly surprised and def will be buying a set for the boat once I make sure there is nothing wrong with the charging or electrical system.