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Using the OutBack FLEXmax with a Battle Born LiFePO4 Battery

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The OutBack FLEXmax is one of the most versatile chargers that we have tested. It has a very intuitive user interface that makes programming it to work with a Battle Born Battery very straightforward.

Tools Needed:

1. #2 Phillips Screwdriver

2. Flat Head Screwdriver

Before starting, make sure to disconnect PV systems that may be powering the FLEXmax.

For clarity,  reference the buttons according to their number in the picture below.

Outback FLEXmax buttons

Step 1:

Unscrew the front panel on the unit using the #2 Phillips screwdriver.

Step 2:

Connect your Battle Born Batteries positive and negative terminals to the FLEXmax’s positive and negative terminals, respectively.

The unit will power on.

Step 3:

Follow through the manual that was provided with the FLEXmax to get to the “Status Screen.”

This is the screen that is in the picture above that displays the voltages coming in and out of the unit.

From this screen, press the 1st button. You will now be on the “Main Menu Screen.”

Step 4:

Press the 4th button labeled “GO” on the screen to select “Charger.” On the “Charger” menu, change each parameter to the following:

  • Current Limit: This will depend on what amplitude you want to charge your battery bank at.
  • Absorbing: 14.4 V
  • Float: 13.4 V

Press the 1st button to exit this screen. Press the 1st button again to return to the “Main Menu Screen.”

Step 5:

Press the 3rd button until  the cursor is to the left of “EQ.”

Press the 4th button to enter the “EQ” menu.

Set the EQ voltage to 14.4 V.

Press the 2nd button to move to the next screen.

Set the battery equalization time to as low as possible.

Then press the 1st button to exit.

By default, Equalization is set to be manually turned on. Be sure to never turn equalization on, as it is not necessary with Battle Born Batteries.

Step 6:

If you are using a remote temperature sensor, disconnect it from both the battery and the FLEXmax. Battle Born Batteries do not need temperature compensation.

Your FLEXmax is now configured to be used with Battle Born Batteries!

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15 thoughts on “Using the OutBack FLEXmax with a Battle Born LiFePO4 Battery

    1. Hi TJ, thank you for reaching out! 29.9 is high and can trigger high voltage cutoff in our batteries. For a 24 volt system we recommend checking parameters. For bulk and absorption, it should have a 28.8 volts output and for float it should be at 27.2. Please disable your equalization if possible, and if not set it to 28.8 volts. If you have any other questions or need more clarification, you can always give us a call at 855-292-2831 and our tech and sales team would be more than happy to help you with this issue.

      1. Hi, For the float voltage at 24v… You say 27.2v. But 13.4 for 12v system… Shouldn’t it be 26.8 for a 24v system; which would be double from the article above at 12v? Please Clarify. Thanks

        1. Hi Bob, thanks for reaching out. We have a range of float voltage values that will work with our batteries. Anything between 26.8-27.6 volts is acceptable to give greater flexibility for our customers charging devices. The sweet spot is 26.8 volts for a 24 volt system. If you have any other questions, please feel free to give us a call at 855-292-2831 or email our tech team at [email protected].

  1. Is there any way to configure the RTS temperature sensor on the Outback to shut off charging at low temperatures as a sort of extra precautionary measure?

    1. Hi Zac, thanks for reaching out! We don’t know of a way to configure this sensor to shut off charging. The RTS is used as a temperature compensation system to assist in charging, but since our batteries don’t need temperature compensation during a charge cycle this device isn’t needed. A call to Outback may reveal another option to use this sensor as a low temp cutoff, but our BMS has this technology built-in and will stop charging to the battery if it is exposed to prolonged cold temperatures.

  2. Hi, I have 4 battleborn batteries – 100ah batteries, what do i set for absorb time, re-bulk voltage, current limit, eq voltage?

    1. Hi Steen, thanks for your comment. For a 12 volt battery bank, we suggest the following settings:
      Absorb time: Set between an hour and a half, and two hours. Our team suggests 20-30 minutes per battery in parallel so it is based on what the controller is able to accept.
      Rebulk Voltage: Set to 13.3V.
      Current limit: Set to 200 amps.
      EQ voltage: Please disable this setting, or set it to 14.4V if you cannot disable it.
      Please let us know if you have any other questions, or give our team a call at 855-292-2831 or send an email to [email protected].

  3. I am running 6 of the 50 Ah 24 V LiFePO4 Deep Cycle Battery in parallel what amperage should I charge them at to get the best life and performance ? also I am going to add 2 more in the future.

    1. Hi Lonnie, thanks for your comment. Our team suggests charging them at 25 amps per battery so you don’t exceed a 150 amp rate. Please let us know if you have any additional questions and we are glad to hear that you’re looking to expand your system!

  4. I’m upgrading from lead-acid batteries for our residential off-grid system, which runs off a 48V MagnaSine inverter and Outback FlexMax 80 charge controller. The plan is to start with a string of four 12V batteries, wired in series, and if needed, add a second string to that in parallel. Just to double-check, would the corresponding 48V-system voltage set points be as follows?

    Absorbing: 57.6V
    Float: 53.6V
    EQ: 57.6V (Noting that lithium-ion batteries shouldn’t need equalization in practice, correct?)

    These come from multiplying your 12V specs by 4, but based on the comments, it sounds like there’s a little range as one strings up the batteries to higher voltage.

    WRT current limit, is 200A still a valid limit for either 4 12V batteries in series, or two such strings?

    Thank you!

    1. Hi Evan, I apologize for the delay in getting back to you. Our sales and tech team suggests the following for 48 V:

      Bulk/absorb 56.8 – 58.4(we usually recommend 56.8v)
      float 54.4 or lower
      No equalization(or set it to 56.8v), no temperature compensation and absorption time is 20-30 minutes per battery string (if it’s an option).

      We would recommend a 50amp charging rate for a 48V 100Ah. The charging rate is based off the Ah size of the configuration.

      If you have any additional questions, please give our sales and tech team a call at 855-292-2831. Thank you!

  5. I purchased 4 100ah 12volt LI batt. from Out back. I have a MX60 PV MPPT Outback system. I am replacing my lead acid batteries. I connected the new batteries and they worked until they got low and shut off but will not recharge. What have I not done right?

    1. Good morning Harold. If you haven’t already, please give our technical sales team a call at 855-292-2831 and they will be able to assist with any troubleshooting issues you may face.

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