At what amperage can I charge my 12v battery bank?

I have four 12v deep cycle lead acid batteries wired in parallel. They are all the same age (1 year old), and each battery is 70AH, for a total bank of 280AH.

My question is, at what amperage is it ok to charge these batteries? I know the lower the better, but I do not have electric at the dock where it is, and would like to charge it at a friend’s dock and only have a few hours there at a time. I often take these batteries down to about 40-50% capacity (which I believe is fine for a true deep cycle battery) before a recharge, meaning this could take 70 hours at 2amps (which I unfortunately don’t have the luxury of doing).

I have an automatic 12v deep cycle charger that has 2, 8, 15, and 100amps for its current output. I figure 100amps is way too much and would risk damaging the battery, but then again it would only be 25amps per battery right? Either way, I am considering buying a new battery charger and would like to find one right around the highest amperage that could safely (and without damage to the battery) charge these batteries.

As an aside, what voltage (I don’t have the reader for specific gravity) would be fully charged for the batteries? They came around 13.2v but I wasn’t sure if that was a special surface charge or not.

These are the batteries -

Thanks all

8 Answers

  • 8 years ago
    Favorite Answer

    If you purchase a new battery charger, it will automatically adjust the charging rate, beginning at about 20 amps. It will have separate outputs. (normally 3 batteries) . If you only have a few hours at a time, you will not come close to fully recharging your 4 batteries. You can "force ' a charging rate of about 20 Amps but I'm not sure the specifics because I don't use that feature.

    What I'd suggest is that you purchase a Solar panel (10 to 15A) and controller for the purpose of topping up and or adding charging time to your current system.

    Fully charged the batteries will be just over 13 volts so your 13.2 V is about right.

    There is something you might try, but it's been a while since I bought one, but it was used on RVs it's called a isolator, it takes the input from a 110A alternator and has 3 outputs. You can connect it to 3 of your battery. It it will charge the weakest battery first then the next weakest until it brings them all up to the same level. I don't know if there are any 4 battery isolators. That way you can use your 100A charger.

    I think you need to have a battery switch so that you can keep then separate except when in use.

  • Anonymous
    4 years ago

    It will support to grasp the scale of the boat, is it a mannequin or a specific 40 footer, why would you have to run the motors when it is on cost, quite what you hope to achieve by way of going to forty eight volts I are not able to even guess at, expectantly you re no longer simply going to put 48 volts by way of a 24 volt motor, the least ypu can hope for is to demagnetise it if not fry the windings. Your step up chargers must be DC-AC-DC as step up transformers can only be AC, so in case you are charging from two seperate batteries by way of step up chargers there should be no concern charging two halves of the forty eight volt bank simultaneously, even when below load, that is if it is a model and you might be charging from two seperate sources, If there is mains worried I can't see how the nescessary seperation will also be done.

  • 4 years ago

    12v Battery Bank

  • 4 years ago


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  • Ned
    Lv 6
    8 years ago

    When people talk about batteries being around 13.2 VDC that is a float charge and they are still on the charger, that is charger on and batteries fully charged 12.6 to 12.9 VDC.

    Charging occurs in stages, batteries will only accept so much even if you are trying to pump 100 amps into the batteries. You can really cook your batteries should you overcharge, the result of too high a voltage not amps.

    Smart chargers are the way to go provided you don't knock your batteries down to low in voltage.

    Next at 280 AH you only have 140 AH available and a 15 amp rate will get it done overnight.

  • Anonymous
    8 years ago

    Deep cycle batteries should be recharged in stages so it would be fine to start off at 100 amps but as the charge comes up the charge rate should be reduced. There are chargers that automatically detect the battery state and change the rate automatically. These are called "smart chargers" and are commonly used for charging caravan batteries.

  • Anonymous
    8 years ago

    100 amps is not too high for a lead-acid battery. It's called a quick charge. When divided by 4 that would be a normal charging rate. Six amps is considered a trickle charge.

    Ask at the marine suppliers about charging regulators. I have heard that most boats use a temperature controlled regulator that makes batteries last fifteen to twenty years, as compared to five or less for car batteries where no temperature control is used. I have no other information, you'll just have to ask and see what you find.

  • Anonymous
    6 years ago

    i have exide xpress mhd 700 type battery for my indigo marina car, so how can charge my battery, that means what is charging current for use to charge

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