Sterling Pro Batt Ultra Battery to Battery Charger

  |   LiFePO4 Charging   |   51 Comments

Applicable Models: BB1230, BB122440 



The Battery to Battery charger made by Sterling Power solves a huge issue that many of us have, charging your battery bank off of your cars alternator. Sterling accomplished this by creating a charger that takes power from the starter battery, regulates the voltage and current, then sends it to the battery bank.


Here is how to set this unit up with Battle Born Batteries!


Before starting this installation, make sure that your vehicle is powered off.


Step 1:

Take unit out of box and remove lower front red face plate to expose the input terminals.


Step 2:

Connect the negative terminal of the house batteries to the negative terminal of the starter battery with a 6 or 8 AWG cable. We used a 6 AWG cable throughout our installation.


Step 3:

Run a positive cable from the positive terminal of the starter battery to the “IN+” terminal of the battery charger.

Run a negative cable from the negative terminal of the starting battery to the “NEG-” terminal of the battery charger.


Step 4:

Bring a cable from the positive terminal of your house battery and connect it to the “OUT +” of the battery charger.

Double check that you have made all of the correct connections and then start the vehicle and the unit will power on.


Step 5:

Once the charger is fully powered on press both of the buttons, “SETUP” and “SELECT”, for 10-12 seconds (10-12 flashes). Then use the left or right button to move the LED up to the “Custom” position. Press and hold the two buttons again for 2 seconds to select this setting.


Step 6:

A LED at the top of the unit will be blinking over “Bulk/Boost”. Use the two buttons to move the LED’s so that both the 14.2V and 14.6V are illuminated. Press and hold the two buttons again for 2 seconds to select this setting.


Step 7:

The “Conditioning” LED will now be flashing. As before, use the two buttons to move the LED’s so that they are illuminating 13.4V and 13.8V. Press and hold the two buttons again for 2 seconds to select this setting.


Step 8:

The “Float” LED will now be flashing. Use the two buttons to move the LED’s so that they are illuminating 13.4V and 13.8V. Press and hold the two buttons again for 2 seconds to select this setting.


Step 9:

Two LED’s at the top of the unit should ow be flashing, the  “Bulk/Boost” and “Float” LED’s. Press the two buttons for two seconds. Now the “Conditioning” and “Float” LED will illuminate. Press and hold the two buttons for two seconds. Press and hold the two buttons for two seconds for the third and final time.

Now you can either press the two buttons again or let the unit sit for 30 seconds to restart it. It will then power off and restart with the correct charging parameters.


Step 10:

If your vehicle does not have regenerative breaking, you can turn it off by pressing the “SETUP” button for 10-12 seconds. You will then see the “Absorption” light blinking. Press the two buttons for two seconds and then wait 30 seconds for the unit to restart.


Step 11:

With the vehicle on, use a multimeter to make sure that the charger is outputting the correct voltages. If it is not, you can reset the unit by following this video.


If you have any issues, please give us a call at 855-292-2831 and we will be happy to help with the process.

  • Steven Peaslee | Mar 8, 2018 at 10:44 pm

    Can you give instructions for the Sterling BB1260
    60 amp unit for runn two 100ah batteries


  • Garrick Boyd | Jun 10, 2018 at 4:00 am

    I see Steven’s question, but don’t see an answer. I have the exact same question. Also, is the Sterling a good choice or a waste of money vs a battery isolator?

    • Sean Nichols | Jun 10, 2018 at 5:10 pm

      Sorry about that, we missed that one. The Sterling product is great, its a step up from just an isolator. Anything 300ah or more, I would consider it.

      We also offer an isolator programmed for Lithium from precision circuits. All depends on how much control you want.

      Please call me 775-221-8894 or email me [email protected] Thanks for reaching out.

  • Dave Stilholme | Sep 7, 2018 at 6:28 am

    If the Sterling unit is recommended for 300AH or more what would you recommend for using only one 100AH battery? Is a B2B charger needed if using only one battery or would the current draw damage the alternator or overcharge the lithium batter? This Sterling unit seems quite large for the space I have to work with. Is there a somewhat smaller alternative for a smaller system?

    • Sean Nichols | Sep 7, 2018 at 10:49 am

      We actually offer 2 choices for managing current flow and alternator charging. We have a special battery isolation manager from Precision Circuits that works really well and takes up very little space and does not require programming. This device will duty cycle your alternator charging current 15 min on 20 min off, to make sure you don’t overheat your alternator on a long drive. This is or the Sterling battery to battery charger work well in banks 300ah or more.

      In smaller batter banks you can just use any isolator, it will work fine. If you want to expand your bank later to 3 or more, put the LiBIM in now and that way you are all set for your future expansion.

      Here is a link to this part

  • Nicholas Wilson | Nov 28, 2018 at 10:24 am

    How do you pair this with a solar charge controller and PV panels?

    • Dianne F | Nov 28, 2018 at 3:50 pm

      Hi Nicholas,

      The Sterling Battery to Battery chargers act as a charging mechanism to properly fill your lithium battery bank via the alternator/starter battery. Solar charging is not involved in this process and is meant to charge from the sun.

      We hope this helps but please don’t hesitate to give us a call if you would like to discuss this further.

      Thank you!

  • Kevin Holt | Dec 3, 2018 at 9:36 pm

    I keep reading all this stuff about modern vehicles have smart alternators now and they don’t charge auxiliary batteries good with a regular charge relay like they used to and I need one of these DC to DC chargers. Is that true or can I just use a charge relay? I have two of your 100ah batteries I’m putting into my 2018 Ford Transit. I’m just wanting to pump some amps into my batteries driving between campsites or possibly running the engine at a campsite without damaging my batteries.

    • Dianne F | Dec 5, 2018 at 3:21 pm

      Hello Kevin,
      2 we recommend charging the batteries with half the amperage of your battery bank. If you have 2 batteries in parallel giving you 200 AH’s you can charge with up to 100 amps. If your alternaotr is pushing more than 100 amps when charging the batteries you muight want to look into a battery to battery charger that limits the amps. If it’s slightly more than 100 say 115 that’s not going to make a difference. But by the time it reaches the batteries the amps may be limited to around 100, so you may be good with a simple relay or solenoid.

      Thank you!

      • Dawn Bustanoby | May 16, 2019 at 11:57 am

        Does this mean that if my alternator is only 90amps (standard VW Vanagon) that I can skip the battery to battery charger? This would be a much more economical and easy install as it would mean my current system is plug and play.

        • Dianne F | May 22, 2019 at 8:40 am

          Hi Dawn,

          As long as you are not going over the recommended charge rate of .5c (50 amps per 100ah battery) then your alternator should provide a good charge to your battery bank. The advantage of the Sterling unit is that it will provide a 3 stage charging profile and disconnect the two battery banks when the alternator is not charging.


  • Dave Garth | Dec 31, 2018 at 7:47 am

    I also have a LTV Wonder motorhome on a 2018 Ford Transit chassis. I want to install two 100 amp hour BattleBorns. I’m still not clear whether I need the Sterling unit or not as I’ve gotten conflicting advice. (I don’t think I have room for it.) My alternator is a “210 amp” alternator, but, I don’t know how many amps it would typically output to the batteries, and I don’t know how I could determine this in advance of installation. I don’t want to unnessarily shorten the life of the new batteries or my alternator. Would the isolator mentioned above be adequate? With an isolator or Sterling unit, can I use the existing cable that is charging my current lead-acid house batteries now (that I assume is connected to an isolator) or do I need to install a new cable direct to the starting battery or alternator? Thanks for your help on this.

    • Dianne F | Jan 8, 2019 at 10:21 am

      Hello Dave,

      The Sterling 60 amp B2B charger is a good choice for a two bank lithium battery setup. This will regulate the current into the lithium batteries and properly isolate the starter battery and the house bank. Its a good chance that without regulating the current coming from the alternator, you will be exceeding the recommended .5c charge rate. Its difficult to make the correct recommendation without knowing how much amperage is coming into the house bank without putting an amp meter on the wires. We could safely assume the existing wire would be ok to use when installing the Sterling device between the battery banks. When you find the amperage that is being delivered to the house bank then you could refer to a wire sizing chart for the correct gauge.

      Thank you

  • Eric Talaska | Jan 1, 2019 at 6:12 am

    Can I restrict the output to 24.4V for a battery that has a max charge rate of 25V? If the output is higher than 24.4, will line loss bring it down to about 24.4?

    • Dianne F | Jan 8, 2019 at 10:31 am

      Hi Eric,

      Your charging voltage for a 24 volt system looks a bit low. For our batteries used in a 24 volt configuration we recommend: Bulk/absorb 28.4 – 29.2
      float 27.2 or lower

      Thank you,

  • John Bell | Jan 3, 2019 at 8:34 am

    Since a “simple relay or solenoid” will continuously connect the starting battery and Lithium when driving, is their a concern of overcharging the Lithium batteries by continuously subjecting them to say 14.4 volts for hours once they are “fully charged”?

    • Dianne F | Jan 4, 2019 at 5:10 pm

      Hi John,

      Subjecting the batteries to 14.4 volts for a few hours, even a few days will not cause damage or problems to these batteries. If you were storing these batteries for months and had this voltage then we would discourage it.

      Thank you,

  • Jim Kelly | Jan 13, 2019 at 11:28 am

    Hi John,

    I have a follow up question from Nicholas about pairing to the solar. When the BB1260 is in operation charging the batteries, can the solar system simultaneously be connected and charging? I’m concerned that this might create a conflict or backfeed situation without some form of isolation.


    • Dianne F | Jan 17, 2019 at 3:10 pm

      Hi Jim,

      If you are charging simultaneously, you will just be increasing the amperage going into the battery bank with this scenario. You will not get a conflict or a back feed from this.


  • Bryan Stephan | Jan 15, 2019 at 8:25 pm

    Will the Sterling Pro Batt Ultra Battery to Battery Charger work just fine for a 100ah lifepo4 battery with a Mercedes Benz sprinter? I’m charging my battery now with (2) 100 watt solar panels and an mppt charge controller. However, I’m hoping on rainy winter days the B2B charger will help support the system. Thoughts?

    • Dianne F | Jan 17, 2019 at 12:36 pm

      Hi Bryan,

      Yes, the 30 and 60 amp versions work great to properly isolate, limit current and properly charge our lithium batteries.

      Thank you,

  • Bryan Stephan | Jan 15, 2019 at 10:34 pm

    Do you need a fuse between the b2b charge and the house/starter batteries?

    • Dianne F | Jan 17, 2019 at 12:34 pm

      Hello Bryan,

      Yes, per Sterling’s installation diagram they are calling for fuses before and after this device on the positive wires.

      Thank you,

  • Darol Hinton | Jan 23, 2019 at 10:58 am

    I am getting mixed messages in things I am reading on line relative to the need for a device like this (Sterling charger) for my Sprinter based RV. It has a 220 amp alternator and I would be putting 2 100AH Battle Born batteries in it. I see “drop in replacement” and I also see that alternators can be overloaded by lithium batteries due to their ability to sink a lot of current while charging due to less internal resistance.

    My first question is how much current are the two discharged batteries in parallel going to be attempting to draw from the charging system assuming no current limiting devices are between them and the vehicle charging system?

    Am I risking damaging my Sprinter alternator with two discharged batteries attempting to charge at the rate they can absorb current without using an intermediate current limiting device?

    Another question. What is the resting voltage of a charged BB battery? I will be using a system to charged the chassis battery when the house batteries are charging from external or solar and need the threshold voltage to turn on the connection.

    Thank you

    • Dianne F | Jan 23, 2019 at 8:09 pm

      Hi Darol,

      The amount of current that the batteries will draw will depend the gauge of wire that feed your lithium bank, what the length of the wires are and what else is drawing current from the alternator. Typically we see 160-190 amps being supplied to a aux battery bank from a 220 amp alternator when the wires are sized correctly. This can vary greatly and the only way to truly know what is being supplied would be with an amp meter on the wires. Our lithium batteries will gladly accept this fast charge even though it is over the recommended 50 amps per battery charge rate. The most significant impact on diminished lithium battery lifespan in R&D testing is not deeply discharging the batteries but rather charging at over the recommended .5c rate.
      Your sprinters alternator has the potential to be overtaxed and suffer pre mature wear over time if you do not use a current regulating device. This is why we recommend the sterling product in applications with one or two lithium batteries and higher amp alternators. In applications with three batteries or more we usually recommend our lithium battery isolation manager(LI-BIM) and this device will duty cycle the charge from the alternator, 15 minutes on and 20 minutes off in order to protect the alternator, allowing it to cool down.

      Resting voltages of Battle Born Batteries:
      13.6V = 100%
      13.4V = 99%
      13.3V = 90%
      13.2V = 70%
      13.1V = 40%
      13.0V = 30%
      12.9V = 20%
      12.8V = 17%
      12.5V = 14%
      12.0V = 9%
      10.0V = 0%

      I hope this is helpful, thanks.


  • David Garth | Feb 1, 2019 at 8:22 pm

    1. What size wire do you recommend between two 100 amp hour BattleBorns?
    2. My Transit has a fused 60 amp 6 ga wire now going to the house batteries from the upfitter takeoff point. Can I use this wire to go to the Sterling input? (Less than 10 feet long.)
    3. How much ventilation does the Sterling unit need?

    • Dianne F | Feb 1, 2019 at 10:31 pm

      Hi David,

      1. Keep the wires short and we usually recommend 1/0 wire for connecting our batteries together.
      2. You shouldn’t get much voltage drop at all with 6awg wire, it is good for 60 amps until you get to about to about 15-20 feet.
      3. Sterling says in their manual to make sure the unit has a well ventilated space and not to cover the vents on the unit, not much more than that. It will shut off if it reaches 131 degrees.


  • jim banning | Feb 6, 2019 at 9:55 am

    Does the Sterling B2B charger also work as a battery isolator protecting me from drawing down the starter battery or do I need to install a separate isolator?

    • Dianne F | Feb 7, 2019 at 8:08 am

      Hi Jim,

      The Sterling B2B chargers will also act as an isolator when installed between two battery banks. This device will replace the existing isolator and properly regulate and also disconnect appropriately. No need for a separate isolator.

      Thank you,

  • Dave S | Feb 7, 2019 at 6:29 pm

    If you had a 100 amp hour battle born battery in your camper could you?
    Use a 50 amp inline fuse from the positive of the vehicle to the positive of the battle born just as a safety breaker. Then discharge you house battery by 80 percent. You could run this for a while and see if it blows or not. If it doesn’t no need to spend the money on the Sterling unit.

    • Dianne F | Feb 8, 2019 at 5:21 pm

      Hi Dave,

      Assuming that you will never get more that 50 amps back to your lithium batteries then hypothetically you could try this. The problem is that you are still connecting a 13.6 volt full lithium battery to a 12.7 volt full lead acid battery together. This would cause the lithium to always want to put a charge into the lead acid battery, essentially never properly isolating the two battery banks. The sterling unit also has a 3 stage lithium charging profile that will handle the charging back to the lithium batteries.


  • Bob Kachnik | Feb 19, 2019 at 9:32 am

    Hi – a few questions. I have 4 Battleborn 100A batteries in a 2016 Sprinter RV.
    1. Looks like Sterling 1260 mode 2 is appropriate for a 2016 Sprinter RV – only on with ignition – right?
    2. What size fuses should be used on the positive wires using the Sterling 1260 model?
    3. Not sure I understand about regenerative braking but I believe this should be disabled for the Sprinter – right?
    4. With the Sterling, is there a way to combine the batteries like with the LI-BIM?
    Many thanks in advance,

    • Dianne F | Feb 27, 2019 at 1:00 pm

      Hi Bob,

      1. yes, if you would like to connect your ignition wire to the sterling unit then mode 2 is appropriate.
      2. Sterling recommends a 100 amp fuse and 6 awg wire for applications 25ft or under.
      3. Correct, regenerative braking does not apply for sprinter vans.
      4. The Sterling B2B chargers are one direction chargers, not a bi-directional like the LI-BIM.


  • Stephen L. | Feb 24, 2019 at 8:12 pm

    Lot’s of helpful information provided here by the team at BB, thank you!

    It’s clear that the Sterling B2B charger will regulate the amperes going from the starter battery/alternator to the BB battery but am I correct in understanding that it will also detect when the aux battery (i.e. the Lithium batt) is fully charged, somewhere around 13.6V? If so, I imagine that if solar was running simultaneously, there wouldn’t be a risk of overcharging the battery since both the B2B and MPPT can detect the battery banks voltage.

    • Dianne F | Feb 27, 2019 at 1:05 pm

      Hi Stephen,

      You are correct, there is no risk of overcharging the batteries when the b2b and charge controller are running simultaneously, they will detect the voltage and charge appropriately.


  • Bruce | Mar 26, 2019 at 2:56 pm

    Many sights I read on suggest that float charging is bad for LFP batteries. Will the Sterling BTB charging profile stop the charging of a LFP battery when it reaches peak voltage or is a float charge cycle mandatory?

    • Dianne F | Apr 16, 2019 at 8:05 am


      Although a float charge is not absolutely necessary, it is also not “bad” for our batteries if you keep the voltage at 13.6 or lower. I believe the float stage is a cycle that cannot be bypassed in the sterling B2B.


  • Steve Rossetter | Mar 26, 2019 at 5:44 pm

    It would be hard to change my wiring from my 7pin trailer style plug input on my slide in truck camper to the camper battery compartment. What is the smallest wire I can safely use with the Sterling b2b unit. I know I’ll have some voltage drop.


    • Dianne F | Apr 16, 2019 at 10:39 am

      Hello Steve,

      On page 5 of Sterlings user manual they list the recommended wire sizes:

      Distance 3m (10 ft) 5m (15ft)7m (22ft) 8m (25ft) 9m (30ft)
      mm2 / AWG 6.0 / 10 6.0 / 10 6.0 / 10 6.0 / 10 10.0 / 8

      Distance 3m (10 ft) 5m (15ft) 7m (22ft) 8m (25ft) 9m (30ft)
      mm2 / AWG 16.0 / 6 16.0 / 6 16.0 / 6 16.0 / 6 25.0 / 4

      Hope this helps, thanks.

  • Stephen L | Apr 17, 2019 at 6:52 pm


    1. Sizing the wire going from vehicle starter battery to Sterling BB1230 input. My van has a 180amp alternator. Using that current (plus my estimated distance of 6-8ft) to calculate the wire results with AWG 2/0. This seems overkill and perhaps to large a diameter to even fit into the Sterling Bat Input. What am I doing wrong here?

    2. I assume the wire gauge suggestions in the manual are regarding the run from the Sterling unit to the aux batteries. I am still unclear if I’m correctly calculating the run from starter batt to Sterling unit.

  • John Wood | Apr 18, 2019 at 12:42 pm

    To Stephen L… The BB1230 only allows 30 amps into it. 30 amps is what you need to size your wire for. I would suggest #8 and put an inline fuse for both input and output (40 or 50 amp or whatever Sterling recommends).

  • Frederick Bucheit | May 19, 2019 at 11:43 am

    I have a single AGM battery– 95 AH, 900 CCA, reserve cap 160 m that I am going to use in a cargo van that I’m converting to a motor home. The van has a special lug for charging house batteries. However, the lug is fused at 60 amps. I want to connect the Sterling BB1260 to that lug and charge my house battery. (1) will that probably blow that fuse? (2) Is there a way I can set the max amps that BB1260 will draw? thanks Fred

    • Dianne F | May 22, 2019 at 8:52 am

      Hi Fredrick,

      Sterling recommends a 100 amp fuse for the 1260 model and hopefully it is easy to replace with your application. You can always ramp back the amperage by setting it to half power mode, you can view how to do this on page 10 of the owners manual.


  • J Bullock | Jun 4, 2019 at 2:05 pm

    Can you please confirm that the Precision Circuits Li-BIM is recommended over a Sterling charger for the following configuration? (I am a little confused by the Jan 23, 2019 comment vs. the Sep 7, 2018 comment.) Metris camper van with 175A alternator, adding two 100 AH Battle Born LiFePO batteries, also connected to two 80W solar panels via an MPPT charge controller, so basically the bundle… So the Li-BIM would be as good or better than the Sterling then? Will one or the other be better for my alternator life or other vehicle/warranty considerations? Thanks.

    • Dianne F | Jun 24, 2019 at 9:35 pm


      for two of our 100 ah batteries and a 175 amp alternator we recommend the sterling B2B charger. The reason is that the current from the alternator will most likely exceed the .5c recommended charge rate for our batteries. In this case the sterling would down regulate the current (to either 30 or 60 amps depending on the model) and thereby charge below the .5c recommendation.

      Thank you,

  • Michael Ruggiero | Jul 24, 2019 at 8:03 am

    I am trying to size a battery system for a truck camper using BattleBorn LIFEPO4. I will be buying a RAM 3500 with the Cummins diesel. A few questions regarding the system sizing and alternator choices:
    1) I can get the truck with a 220A alternator or the dual 220A (440A total). For 4 or 5 100Ah batteries, is the dual alternator setup overkill even if I am looking at adding truck accessories like LED lights, air compressor, and a winch?
    2) With the single or dual alternator setup, will the Sterling 1260 B2B charger limit the charge amps to all the batteries at 60A total? So if I have 500Ah battery bank, then it could safely accept 250A charge at 0.5c charge rate, but if I understand correctly the charger will limit it to 60A? This would be using the proper wire gauge for the amps allowed and wire length.

    • Dianne F | Jul 24, 2019 at 10:32 am

      Hi Michael,

      The 220 amp alternators(when properly wired) can put a lot of current into our batteries quickly. We usually see about 180 amps max going into the batteries from a 220 amp alternator after supplying power to the electronics and charging the starter batteries. This would mean that in 3 hours of running your alternator you would bring our 500ah lithium battery bank from empty to full. It would seem like the dual alternator setup would be a bit of an overkill.

      For a 500ah Battle Born bank, you would limiting the charge to 60 amps when using the sterling and you probably would not need this device for your setup as you would want more amps to come through. You may want to use the LI-BIM or a simple RV/Isolaor solenoid that would allow 200-300 amps to passthrough.

      Hope this helps!

      Thank you

  • Craig McCann | Aug 18, 2019 at 11:28 am

    Hello, currently working on a design that will install two 100Ah B2B Li as house batteries in an RV. May expand house bank to 400Ah at some point. House loads will include smallish 12V loads plus a Magnum MS2012 to run 1000W microwave, TV, etc. Charging sources will be via MS2012 when connected to shore power, vehicle alternator, and future 400W solar.
    Regarding the need for a Sterling BB1260. Currently the vehicle alternator is only 145A. Running vehicle loads total approx. 40A, so roughly 100A for house battery charging if we want to tax the engine alternator to its max. I understand that the two 100Ah B2B Li will have no issue with that amount of current, and also that it may be wise to current limit or time out control the alternator output to prevent alternator wear/failure.
    The question is; Alternator output is regulated at 13.6VDC. It appears the BB1260 will boost output voltage to 14.2-14.6VDC bulk that B2B Li wants. If no boost converter (BB1260) is employed and bulk volts never goes higher than 13.6VDC as regulated by the alternator, what’s the net affect on the battery when the alternator is the only charge source available?

    • Dianne F | Sep 11, 2019 at 1:52 pm

      Hello Craig,

      If you will not be using the sterling and relying solely on the 13.6 volt alternator then you will only receive a slow charge to the batteries. Also, you may never see the batteries get into the full state. At just over 14 volts our bms activates the passive balancing feature in order to keep the batteries as healthy as possible for long term use and you would not be able to take advantage of this feature.

      Thank you,

  • JCalhoun | Sep 12, 2019 at 6:30 am

    I followed your steps to specify a custom profile for the Sterling BB1230.

    If I disconnect all power to the Sterling BB1230, does the custom profile remain? I was unable to find the answer from the manual.

    • Dianne F | Sep 17, 2019 at 12:10 pm

      Hello JCalhoun,

      The custom profile should remain in the Sterling device even after a loss of all power is experienced.

      Thank you,

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