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Thread: Change from Lead-Acid to Li-Ion batteries

  1. #1
    Join Date
    Sep 2017
    Boat: Croatia; Living in Tokyo during the months not on the boat

    Default Change from Lead-Acid to Li-Ion batteries

    The problem I have on board is the storage of electrical energy. Beside the alternators of the engines and a genset, I have 1kWp solar power and a wind turbine.

    I have 5x 100Ah lead-acid batteries for service purposes (engine batteries are separate), from which I can draw a max of 100Ah without damaging the batteries. When charging I have a the first a high and then a very low charging current to charge the batteries without damaging them.

    1. What is your experience with changing to Li-Ion batteries?
    2. Can solar panel controllers be replaced for Li-ion suitable ones?
    3. Is it necessary to also replace the inverter-charger unit?
    4. To which charging level can Li-Ion batteries be discharged to not damage them?
    5. What are charging currents and times to reach 90-95% recharging level?
    6. What kind of Li-ion battery maintenance is needed and how often per year?
    7. What are other experiences you made when changing to Li-ion batteries?
    8. What is your experience in using Li-ion batteries?
    9. What kind of experience did you make with other types of batteries and how much energy can be used without damaging the batteries?

    A lot of questions, I know. I appreciate your answers a lot.

  2. #2
    Join Date
    Jul 2009
    currently Columbia/Panama

    Default Re: Change from Lead-Acid to Li-Ion batteries

    The best place to start is here:

    1. It has been the best modification we have done to the boat, and that is taking into account a lot of modifications including watermaker and washing machine.
    2. Yes, of course they can be replaced, but they may be fine as is. All charge sources simply need to be able to be user-adjustable for LFP voltages. If your solar controllers can be adjusted to, or have a charge profile of, 13.8-14.0V bulk charging, followed by 13.2-13.4V float, then they are good to go.
    3. Depends like #2. If yours has a user-adjustable or set charge profile like described, it will be fine.
    4. For real world application, most people only discharge their LFP bank to 20% SOC (80% discharged) before charging again. Technically, they can be brought to complete discharge regularly, but that would be with laboratory conditions.
    5. LFP will take high charge rates up to 1C (400A for a 400Ah bank), but few people have enough charging sources to provide that rate. Since LFP will take full current right up to being 100% SOC, and has almost no inefficiency, the time it takes to reach full charge will depend on how much charge you can throw at it. If you have a 100Ah battery at 50% SOC, and a 50A charger, then the battery will be full in 1hr.
    6. I've never done any maintenance on ours in over 3yrs of existence other than to check terminal connections occasionally.
    7. LFP doesn't experience much voltage sag under load, nor voltage drop over discharge. They sit at 13.1-13.3V throughout their discharge range, under all reasonable loads. Everything running off DC on the boat will love this. Your watermaker will be more efficient and produce more water, your MPPT solar will produce more power, and you can easily run AC appliances off the inverter without worry. We run our waterheater off the inverter, as well as our large AC-powered watermaker - the batteries don't even blink under 100A loads.

    Read the link I posted, then do some more research. Many people are going with popular "drop-in" battery systems that are not suitable for boats. They are finding this out the hard way, so there are some gotchas to avoid. Don't do your learning off youtube cruising boats - most of them don't know what they are doing. However, there are also good manufacturers of "drop-in" that provide proper systems. These are much more expensive. Finally, there is DIY, which is inexpensive, but one should fully understand what they are doing.

    Mark Cole
    Manta 40 "Reach"

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