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Thread: Battery charging question

  1. #1
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    Default Battery charging question

    I've got (2) 12 volt batteries wired in series to power my 24V electric motor. I've got an onboard dual battery charger. At present, I have one set of leads to one battery and the second set of leads to the second battery. I leave them wired in series as I charge and everything is fine.
    Here's my question. While still wired in series to 24V, can I just use one set of leads, hooking the positive wire to the positive pole on one battery and the negative wire to the negative pole on the other battery? Will this work? I know it would slow down charging time, but will it do any harm?
    The reason I ask is that I'd like to add a second set of batteries to extend cruising time and to simply have as a backup. It would be nice to use the existing dual battery charger for both sets of batteries rather then having to buy a second one.
    Thanks for your wisdom.
    I was born on a wooden boat that I built myself.

  2. #2
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    Default Re: Battery charging question

    Quote Originally Posted by Rich Jones View Post
    I've got (2) 12 volt batteries wired in series to power my 24V electric motor. I've got an onboard dual battery charger. At present, I have one set of leads to one battery and the second set of leads to the second battery. I leave them wired in series as I charge and everything is fine.
    Here's my question. While still wired in series to 24V, can I just use one set of leads, hooking the positive wire to the positive pole on one battery and the negative wire to the negative pole on the other battery? Will this work? I know it would slow down charging time, but will it do any harm?
    The reason I ask is that I'd like to add a second set of batteries to extend cruising time and to simply have as a backup. It would be nice to use the existing dual battery charger for both sets of batteries rather then having to buy a second one.
    Thanks for your wisdom.
    No.
    Because a 12V charger won't charge a 24V battery.

  3. #3
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    Default Re: Battery charging question

    I just bought this...

    IMG20180903114755.jpg

    Not overly expensive... and would solve your problem
    "Travel is fatal to prejudice, bigotry and narrow-mindedness, and many of our people need it sorely on these accounts. Broad, wholesome and charitable views of men and things cannot be acquired by vegetating in one little corner of the earth all one's lifetime" Mark Twain... so... Carpe the living sh!t out of the Diem

  4. #4
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    Default Re: Battery charging question

    No.
    Because a 12V charger won't charge a 24V battery.
    Right. You'd need a 24-volt charger to connect it as you propose. Check your chargers specs, some are 12/ 24 volts, so you may be able to use it.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  5. #5
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    Default Re: Battery charging question

    This may help... https://www.nyc-arecs.org/batt1.pdf

    Specifically, fig.10 and fig.12 on pages 7 thru 12.


  6. #6
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    Default Re: Battery charging question

    Thanks all. Very helpful info and my question has been answered. My best course of action is to buy another dual battery charger for that second bank unless I can find one that is will charge two 24V batteries.
    I was born on a wooden boat that I built myself.

  7. #7
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    Default Re: Battery charging question

    If they are deep cycle batteries (not just regular car batteries) do you want us to tell you how using an automotive battery charger is hurting them?

    How about how combining old & new batteries will quickly bring the new ones down to the same ability to hold a charge as the old ones?
    "If it ain't broke, you're not trying." - Red Green

  8. #8
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    Default Re: Battery charging question

    Quote Originally Posted by Garret View Post
    If they are deep cycle batteries (not just regular car batteries) do you want us to tell you how using an automotive battery charger is hurting them?

    How about how combining old & new batteries will quickly bring the new ones down to the same ability to hold a charge as the old ones?

    I know that using a regular ol' automotive charger isn't good for deep cycle batteries. So what should I get? My batteries are rather small: 12 volt, 35 amp.

    Thanks.

    Jeff

  9. #9
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    Default Re: Battery charging question

    Quote Originally Posted by Garret View Post
    If they are deep cycle batteries (not just regular car batteries) do you want us to tell you how using an automotive battery charger is hurting them?

    How about how combining old & new batteries will quickly bring the new ones down to the same ability to hold a charge as the old ones?
    I'm using an onboard battery charger made for deep cycle batteries. I also knew about the taboo of pairing mismatched batteries in series.
    I was born on a wooden boat that I built myself.

  10. #10
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    Default Re: Battery charging question

    Quote Originally Posted by jpatrick View Post
    I know that using a regular ol' automotive charger isn't good for deep cycle batteries. So what should I get? My batteries are rather small: 12 volt, 35 amp.

    Thanks.

    Jeff
    What kind of battery? Lead Acid, Gel AGM, Lithium?
    "If it ain't broke, you're not trying." - Red Green

  11. #11
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    Default Re: Battery charging question

    Quote Originally Posted by Rich Jones View Post
    I'm using an onboard battery charger made for deep cycle batteries. I also knew about the taboo of pairing mismatched batteries in series.
    Good to hear Rich - just had to be a PITA

    I learned the old with new issue the hard way: at my old place, which is off-grid & runs off batteries & an inverter, I added 2 new $400 batteries to my 5 year old bank. Got an extra day+ cycle out of them at first & within a month or 2, it'd dropped to marginally better than before I spent $800.
    "If it ain't broke, you're not trying." - Red Green

  12. #12
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    Default Re: Battery charging question

    Quote Originally Posted by Garret View Post
    What kind of battery? Lead Acid, Gel AGM, Lithium?

    Sorry... they are SLA/AGM.

    Jeff

  13. #13
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    Default Re: Battery charging question

    Quote Originally Posted by jpatrick View Post
    Sorry... they are SLA/AGM.

    Jeff
    NP - you knew - so it was obvious, right?

    Most batteries (except Lithium) should have a 3 stage charger: Bulk, Absorption, Float. However, many AGM do not want to be Floated (which is not done every time you charge anyway). What voltages for each stage also vary. Best thing would be to check with the manufacturer of your battery. Proper charging will keep the battery's capacity & (greatly) prolong its life expectancy.
    "If it ain't broke, you're not trying." - Red Green

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