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  • Deep Cycle Batteries

    My inverter will shut off at 10.5 volts. Therefore my batteries will never get below 10.5 volts. I'm guessing that getting a deep cycle battery is a waste of money. Am I thinking this through right?

  • #2
    No you are not.

    Deep cycle has to do with how the battery the plates are designed, not the voltage they can drop to when discharged.

    WWW

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    • #3
      Originally posted by silverfish View Post
      My inverter will shut off at 10.5 volts. Therefore my batteries will never get below 10.5 volts. I'm guessing that getting a deep cycle battery is a waste of money. Am I thinking this through right?
      Not even close to being right.

      A deep cycle battery even if you were to abuse them down to 10.5 volts would at least have a few hundred cycles. A SLI or starting battery only a few cycles.

      Now here is a clue for you Batman. A 12 volt battery is at 0% charge at 11.9 volts.
      MSEE, PE

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      • #4
        Still a bit lost. Do I need to go for the deep cycle or a standard battery if my inverter shuts off at 10.5 volts?

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        • #5
          Where the inverter shuts off has nothing to do with what type of battery you need.

          I'll say soley because you are using one tells me you need a deep cycle.

          WWW

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          • #6
            Yes, you want a deep-cycle battery.

            Re - your inverter cutoff at 10.5v:

            Zero volts, in case that is what you are thinking, is *beyond* fully discharged and well into damage territory. Normally one tries not to go below 11.9v or so and is considered a fully discharged battery. Round it to 12v to make it easier to remember. The 10.5v cutoff of your inverter is more of a dead-man protection against taking it way too far. Damage is happening, but it won't be catastrophic like it would be by taking it down to nothing.

            If you rely on your inverter to always cut you off at 10.5v you will be eating up your cycle life and performance. What this means is that if you want to get any sort of cycle life out of it, do not go below 12v which implies some sort of monitoring or calculation of your power needs.

            This is a common beginners mistake of relying on the inverter cutoff as a normal daily routine. You should be cutting it off well before that at 12v or higher.

            So why do inverter manufacturers not just set a cutoff of 12v instead? That is because if you are pulling heavy *temporary* loads, like from a bandsaw, huge drill motor and the like, there will be a large voltage drop temporarily, and that might be slightly below 12v for a very short time, and will recover.

            Basically the moral of the story here is yes, use a deep cycle battery, but do not rely on your inverters cutoff to be a hands-off solution. It is only there to prevent catastrophic damage, and if you are hitting that, you need to re-examine your setup to stop before that.

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            • #7
              Originally posted by silverfish View Post
              My inverter will shut off at 10.5 volts. Therefore my batteries will never get below 10.5 volts. I'm guessing that getting a deep cycle battery is a waste of money. Am I thinking this through right?
              The 10.5V cutoff is to protect your system. If you will not be draining your batteries often, deep cycle batteries will last you a very long time so the extra initial investment is worth it in the long run. Imho AGM is currently the way to go (for now).

              This year I upgraded my bank to 8 VMAX AGM Deep Cycle SLR Series batteries (SLR125 model) because sometimes I will drain the batteries pretty far down. My previous bank consisted of Trojan flooded batteries, got tired of maintaining them plus it was time for an upgrade. The VMAX batteries are built to handle the abuse. They use tin-lead alloy plates vs. calcium lead alloy plates found in most other lead acids.

              I thought about going Li-Ion but the cost is still too high, so far I'm happy with my VMAX Solar batteries.

              Regards,
              positiveenergy

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              • #8
                Originally posted by PositiveEnergy View Post
                The 10.5V cutoff is to protect your system. If you will not be draining your batteries often, deep cycle batteries will last you a very long time so the extra initial investment is worth it in the long run. Imho AGM is currently the way to go (for now).
                Not if you value your money and cycle life. AGM cost twice as much as FLA and last half as long. So over the life of the battery AGM cost 4 times as much.
                MSEE, PE

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                • #9
                  Originally posted by Sunking View Post
                  Not if you value your money and cycle life. AGM cost twice as much as FLA and last half as long. So over the life of the battery AGM cost 4 times as much.
                  Thank you for your input.

                  Its all relative, for my use AGM is worth the money (plus I got a great deal through amazon, shipped for free right to my doorstep).

                  -PositiveEnergy

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                  • #10
                    Originally posted by arpit.v7
                    Here you will get an idea about battery sizing and type <malicious site link removed> Thanks
                    Eat Chit and Die.
                    Last edited by inetdog; 08-09-2015, 03:37 PM.
                    MSEE, PE

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                    • #11
                      I know the Sears Platinum AGM's at 11.9v is at 25% capacity. Those are used for vehicles thou.

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                      • #12
                        Sears Platinum AGM's are re-badged Enersys / ODYSSEY pure-lead batteries. They are excellent agm's, having much lower internal resistance than conventional agm's. (Optima's and a few other manufacturers of pure-lead are similar). That low IR is really a life-saver in areas of low solar insolation where you can hammer them with large solar arrays in a minimal amount of time if needed.

                        If the consumer type Sears Platinums / Odyssey batteries are just too small, consider the Outback or Enersys SBS line of agm's.

                        As always though, make SURE you don't under-charge an agm.

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