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  1. #1
    King Pin
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    Lithium Battery Owners - Some Useful Data

    I recently purchased two Battle Born 100 amp hour lithium batteries for my 2017 Grand Design 297RSTS. Ginnie and I do a lot of camping without hookups, so we wanted to have as much battery power as possible without a lot of weight on the tongue of the trailer. I'm a retired electrical engineer, so when I make a purchase of this size, I like to have data to understand how to get the best results from the items I spend my money on.

    State of Charge Tables

    No matter what type of battery you have, it's important to know the state of charge. On lead/acid and AGM batteries, you should never let them get below 50% state of charge or you risk damaging the batteries and shortening their life. So if you have a 90 amp hour battery, you should use no more than 45 amp hours before recharging. It's easy to monitor the state of charge by measuring the voltage on your batteries with a volt meter. To get an accurate state of charge measurement, it should be taken when there is not a load on the batteries. This means that you should turn off all items that are draining the battery (such as lights) for at least 10 minutes before taking the measurement. If you're using lead/acid or AGM batteries, you should recharge the batteries when they reach a no load voltage of 12.10 VDC which is a 50% SOC. The batteries will last even longer if you try to keep them above a 70% SOC which is a no load voltage of 12.37 VDC. The following table shows the corresponding voltage for a 50% state of charge on an average lead/acid or AGM battery:


    Lead/Acid - AGM SOC Chart

    However, my new batteries are Lithium, Iron, Phosphate (LiFePo). Depending on the brand, you can use nearly all of the capacity of a LiFePo battery without damage. So on my 100 amp hour battery, I can use the full 100 amp hours and not damage the battery. The battery has a built in battery management system that will shut off the battery once it has been depleted. However, I still want to know what the state of charge is so that I don't run out of power and I know when it's time to recharge the batteries. I contacted Battle Born batteries and they provided the following information for their 12 VDC, 100 amp hour battery:


    LiFePo SOC Chart

    Lithium Iron Phosphate Battery Charging

    Battle Born batteries advertises that you can charge their batteries with the converter/chargers that come standard on most RVs. But they do state that the LiFePo batteries will charge much faster with a converter/charger that is built specifically for lithium batteries. Recently, I took our first trip with the LiFePo batteries. Due to cloud and tree cover, I could not use solar to charge the batteries, so I had to rely on my generator to charge them through the converter/charger that came with the unit. My unit came equipped with a WFCO 9855 converter/charger. It has a Boost voltage of 14.4 VDC, Absorption of 13.6 VDC, and Float of 13.2 VDC. I'd run the generator for 4-5 hours a day, but the LiFePo batteries would only get up to about a 70-90% SOC. So I began researching lithium dedicated converter/chargers to see what the difference would be. Fortunately, I was able to get in touch with the technical staff at Progressive Dynamics who manufactures both standard and lithium converter/chargers.

    Progressive Dynamics had just finished running some experiments on charging 100 amp hour lithium batteries with both a standard RV converter charger (Model PD9260), and one of their units that is designed for Lithium batteries (Model PD9160AL). Lithium dedicated chargers do not have the Boost, Absorption, Float voltages that a standard charger does. They have a fixed 14.6 VDC charging voltage. When the batteries are charged, the voltage remains at 14.6 VDC, but the current tapers off to zero amps.

    The next chart shows the results of charging a 100 amp hour lithium battery with the standard PD9260 charger. If you follow the green line, you'll see that it took approximately 441 minutes for the battery to be fully charged to near 100%. That is almost 7-1/2 hours, and is in line with what I was seeing when I tried to charge my batteries.


    Lithium Battery Charging with a Standard Converter/charger.

    The next chart documents the results of Progressive Dynamics charging test using their lithium dedicated charger. The battery was fully restored at approximately 115 minutes which is just under two hours. This is 5-1/2 hours faster than using a standard charger!


    Lithium Battery Charging with a Lithium Dedicated Converter/charger.

    Summary
    Owners with Lithium batteries can obtain the best results by using SOC charts specifically for lithium batteries. And for approximately $250, you can purchase a lithium dedicated charger which will greatly reduce the time it takes to charge the lithium batteries to their full capacity.



    Note: I'd recommend against purchasing the Progressive Dynamics PD9160ALV through Amazon. I attempted to purchase mine through there. However, the seller (Boat and RV Accessories) shipped a PD9160A (non lithium) charger. And in order to return the item for refund, I had to pay for shipping even though it was their error. I have re-ordered the PD9160AL from Randy at Best Converter and he was very helpful. I should receive it soon and complete the installation.

    Jim

  2. #2
    Long Hauler D2Reid's Avatar
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    Excellent write up Jim, thank you. My first thought was I could use the Lithium Ion dedicated converter on my lead acid 6v batteries. But then I got thinking that loading them with constant 14.6v charge would probably just boil them. I took not that you were an electrical engineer. Do you mind answering questions from us uneducated folk?
    Dallas
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  3. #3
    Big Traveler
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    I'm looking at this and wondering how happy the 12VDC appliances and circuit boards are going to be at nearly 14.5VDC. It seems that usually these appliances are seeing between 12.5 and 13.5 volts during operation. Are they robust enough to handle the extra voltage for prolonged periods of time?
    Jim & Georgianne
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  4. #4
    Paid my dues 😁 FT4NOW's Avatar
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    This is excellent information! I was unaware there were lithium specific converters. Great to know if I decide to add a solar setup or change out my battery in the future.

    Sent from my SM-G950U using Tapatalk
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  5. #5
    King Pin
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    Quote Originally Posted by J&G garage View Post
    I'm looking at this and wondering how happy the 12VDC appliances and circuit boards are going to be at nearly 14.5VDC. It seems that usually these appliances are seeing between 12.5 and 13.5 volts during operation. Are they robust enough to handle the extra voltage for prolonged periods of time?
    Jim - The 14.6 VDC is the unloaded voltage. As soon as a load is applied, the battery management system regulates the voltage to 13.6 VDC (Maximum). You can see from this chart the LiFePo discharge rate for 10, 30 and 50 amp hour draws.



    Jim

  6. #6
    King Pin
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    Quote Originally Posted by D2Reid View Post
    Excellent write up Jim, thank you. My first thought was I could use the Lithium Ion dedicated converter on my lead acid 6v batteries. But then I got thinking that loading them with constant 14.6v charge would probably just boil them. I took not that you were an electrical engineer. Do you mind answering questions from us uneducated folk?
    Dallas - Yep, even though it's not very efficient, you can use a standard charger on LiFePo batteries. But it could result in catastrophic battery failure if you were to use a lithium charger on a lead/acid or AGM battery.

    Jim

  7. #7
    Big Traveler
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    Quote Originally Posted by TucsonJim View Post
    Jim - The 14.6 VDC is the unloaded voltage. As soon as a load is applied, the battery management system regulates the voltage to 13.6 VDC (Maximum). You can see from this chart the LiFePo discharge rate for 10, 30 and 50 amp hour draws.



    Jim
    It would seem that if the charger was on you would be working with 14.6 volts as that is the voltage the charger is applying to the coach.
    Jim & Georgianne
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  8. #8
    Site Sponsor gbkims's Avatar
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    Thanks for the info Jim,

    Caught my eye that the 14.4V Lithium charge voltage matches the PD9200's Boost Voltage you can manually select with their charge wizard pendant.
    PD9200 SERIES OWNERS MANUAL
    Click image for larger version. 

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    Gene
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  9. #9
    Seasoned Camper
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    You may be interested in this interview with the Battle Born principals. Also, if you hit their youtube channel they have a great series on using a battery from a tesla wreck in his RV. https://youtu.be/s64CuK5Yy_o

  10. #10
    King Pin
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    Quote Originally Posted by J&G garage View Post
    It would seem that if the charger was on you would be working with 14.6 volts as that is the voltage the charger is applying to the coach.
    Now you have me thinking.... Dang it!
    But you also have 14.4 to 14.6 VDC when your standard converter goes into boost mode.

    Jim

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