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kp4's avatar
kp4
Explorer
Nov 03, 2013

Battery Charging woes

Bought 2 new deep cycle 12V coach batteries in March.

We went on a 1 week dry camping trip in July.

Ran the generator for probably 2 hours per day on that trip. The batteries steadily discharged to the point where they would not start the generator. Had to start the truck engine to start the generator.

We have not been using the MH much but I decided to check in to this yesterday as it bugs me.

BTW I always disconnect the coach batteries while the MH sits. Also connect them and start the generator and MH engine every 2 - 3 weeks.

I did these "tests" (sorry I don’t think I can use any fancy “formatting”)

B1 = under hood coach battery
B2 = compartment coach battery
T1 = truck battery


Static Check Voltage
B1 11.43 B2 11.35 T1 12.26

Connect to shore power for a few hours
B1 12.6 B2 12.6

Disconnect shore power, connect and run generator
B1 12.7 B2 12.67

Turn off generator, run truck engine
B1 13.85 B2 13.5 T1 14.76

Ran truck engine for 30 minutes
B1 13.3 B2 13.2 T1 14.16

Next morning static voltage
B1 11.93 B2 11.94 T1 12.5

I found a table on the net that says
State of charge at volts
100% 12.6V+
90% 12.5
80% 12.42
40% 11.9

So my 2 coach batteries (new in March) after charging yesterday are at 40% and they will drop more. My truck battery seems to stay at about 90%.

When connected to shore power or generator power the max “charging” voltage I see is 12.6V. The alternator on the truck engine seems to charge all the batteries at a higher voltage.

My truck battery, which is older and NOT deep cycle, holds a charge much better than the 2 coach batteries.

Questions:

Should the gen or shore power charge at a higher voltage measured at the battery terminals?

Is my inverter/converter not doing its job properly? Should it be “letting” the batteries get a bit of an overcharge like the truck alternator does?
Class C
  • RoyB's avatar
    RoyB
    Explorer II
    Nov 03, 2013
    It certainly looks like you may have a static drain or something turned "ON" in the trailer side. They should not drop that much overnite. NOTE I just now saw the comment you only have 12.6VDC charging your battery when shore power is on. It should read 13.6VDC.

    I have one of the CLAMP-ON DC Current meters from SEARS where I can clamp around the battery cable and read how much current is being drawn when I think I don't have anything turned on. If I see more than 1AMP of DC Current being drawn I start tracking down the source of what is on inside the trailer.


    Of course this could also be a bad cell in battery as well...

    I suspect you have something "ON" inside the trailer drawing the power. With the DC CURRENT METER clamped around the battery terminal cable you can start pulling the ATC fuses one at a time and see which circuit drops the current flow.

    Roy Ken
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Nov 03, 2013
    What Brand/model of converter/charger do you have (or inverter/charger).

    The 'charger' output while on shore power or generator is low.....
    Connect to shore power for a few hours
    B1 12.6 B2 12.6

    Disconnect shore power, connect and run generator
    B1 12.7 B2 12.67

    You are seeing higher voltage when running engine.....but the charge line is small so charging of batteries would take hours.

    Need to test 'charger' output with battery cables disconnected.
    With 110V AC power in.....charger output should be 13.6V DC. Anything less 'charger' is not functioning properly.

    Also check that you didn't connect battery cables backwards and the 'reverse polarity' fuses on converter/charger are blown.
    If they are blown the charger output can't get to batteries.
  • kp4's avatar
    kp4
    Explorer
    Nov 03, 2013
    Thank you for the replies!

    Don't know the brand/model of the converter. I have manuals for everything in the MH except of course that. I need to dig in there and look at it.

    I will connect to shore power with batteries disconnected and test voltage, then report back.

    Battery cables are not backwards.

    I "feel" like the converter is under charging. As stated it should be 13.6 while charging and it isn't.

    But I also thought that the converter would either just work or not work. But I suppose that is not the case. It is charging, just not high enough voltage???



    Old-Biscuit wrote:
    What Brand/model of converter/charger do you have (or inverter/charger).

    The 'charger' output while on shore power or generator is low.....
    Connect to shore power for a few hours
    B1 12.6 B2 12.6

    Disconnect shore power, connect and run generator
    B1 12.7 B2 12.67

    You are seeing higher voltage when running engine.....but the charge line is small so charging of batteries would take hours.

    Need to test 'charger' output with battery cables disconnected.
    With 110V AC power in.....charger output should be 13.6V DC. Anything less 'charger' is not functioning properly.

    Also check that you didn't connect battery cables backwards and the 'reverse polarity' fuses on converter/charger are blown.
    If they are blown the charger output can't get to batteries.
  • YC_1's avatar
    YC_1
    Nomad
    Nov 03, 2013
    Some early model converter/chargers would only supply about 3 amps charging current. They would use a relay to isolate the batteries and supply plenty of power to the rv but very little charging power.

    Hence, as others are suggesting. We really need the model number from your converter.

    In any case, no matter its model number, it is not doing the job. Your voltage readings are excellent info.
  • MNtundraRet's avatar
    MNtundraRet
    Navigator
    Nov 03, 2013
    You are talking about at 19+ year old motor-home. How long have you owned it?

    Have you replaced the original single-stage charger with a more modern 3-stage charger? If not there is no way you could go dry-camping for a week with only a 2 hour charge on the batteries each day. The original charger would have required 12 to 24 hours to fully recharge the batteries.

    Your mode of checking and charging batteries does not cut it (an hour or to charging every few, or more weeks).

    If you have checked and cleaned all connections: battery, alternator, grounds, found on the 12v circuit, the single stage charger should have increased the voltage from starting charge (unplugged for 12 hours) from 11.9 volts (whatever) to around 13.6 volts with in a short time to show that it is charging. Then you would have had to continue to charge for 12 to 24 hours.

    The MH engine and alternator should increase the voltage to 14 to 15 volts when read with a multi-meter at the battery-terminals. All reading should be done here for best accuracy.

    Using a clamp-ammeter (reading done at one of the battery-cables next to battery) should show a 20 to 50 or more amps from alternator; 10 to 15 amps from single stage charger, rated charge of 3-stage chargers (45, 55, 60, etc.). This would be expected from any batteries being discharged to 70%soc or less.

    If you can't see at least 13.5 volts charging (any mode) the converter/charger is shot, or bad connections as mentioned. If this MH is new to you I would get the system checked by a qualified technician.

    I suspect your two new batteries from April are close to being goners from sulfation taking place from improper charging.
  • tenbear's avatar
    tenbear
    Explorer
    Nov 03, 2013
    Old-Biscuit has it right. Here are a few other thoughts.

    Running the generator for 2 hours a day is probably not enough to recharge the batteries, especially if you do not have a smart converter. Fully charging your batteries using a voltage of 13.6v will take several days.

    After charging a battery the battery will have a "surface charge" and will read a higher voltage than is really true. It leaks off if you put a load on the battery, or let the battery sit for a while.

    The reason your truck battery appears to hold a charge better is that it is being charged at a voltage well over 14 volts and never really gets discharged. The coach batteries are constantly being drained and are not being adequately charged.
  • Bobbo's avatar
    Bobbo
    Explorer II
    Nov 03, 2013
    I concur. A bad or inadequate charger has killed your batteries. Both batteries and converter/charger will most likely need to be replaced.
  • tenbear's avatar
    tenbear
    Explorer
    Nov 03, 2013
    kp4 wrote:
    .... I "feel" like the converter is under charging. As stated it should be 13.6 while charging and it isn't...


    The converter may well be putting out 13.6v but due to the high charging current with the batteries discharged and the long and possibly small converter to battery wiring, the voltage drop in the wire is causing the voltage at the batteries to be much lower.
  • Bordercollie's avatar
    Bordercollie
    Explorer
    Nov 04, 2013
    Make sure that the heavy guage wires from converter output are securely connected at the converter, usually with set screws tightened with an Allen wrench onto stripped wire ends. Check all connections at house batteries and auxiliary battery switch relay. Make sure converter is plugged in and getting 110vac power.

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