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  1. #1
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    Jul 1999
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    Glen Iris, Vic, Australia
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    Default How do I discharge multiple Makita Li-Ion 3ma batteries to 50% (18v) safely?

    Need latest advice on discharging multiple Makita Li-Ion 3ah batteries to 50% (18v) safely.

    I've got 10 3ah batteries.
    Always, fully charged.

    I'm a bit busy over the next 4 to 5 weeks so won't be able to top up on a regular basis.

    For long term storage, I've read you should store the Makita 3ah hours at 50% (18v).
    Where full is 100% (~23v).

    I don't want to just lock the trigger down on a drill to drain the battery.
    As I'm wary it will shorten the life of the drill.

    Any other options to drain the battery safely?
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

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  3. #2
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    Apr 2011
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    se Melbourne
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    Default

    Not sure how to get to 50%, but use another item for a period to discharge battery. I have a radio (I once left on overnight to drain battery) and a couple of torches that can be safely left on.
    If you want a loan of a spare torch (or two) please send me a PM.

  4. #3
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    Default

    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  5. #4
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    back in Alberta for a while
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    Default

    Quote Originally Posted by barrysumpter View Post
    Need latest advice on discharging multiple Makita Li-Ion 3ma batteries to 50% (18v) safely.

    I've got 10 3ma batteries.
    Always, fully charged.
    TEN ! that would be enough juice for how many days of work?



    Quote Originally Posted by barrysumpter View Post
    I'm a bit busy over the next 4 to 5 weeks so won't be able to top up on a regular basis.

    For long term storage, I've read you should store the Makita 3ma hours at 50% (18v).
    Where full is 100% (~23v).
    it would pay to check the definition of "long term storage". It could well be time periods in excess of 2 years.
    regards from Alberta, Canada

    ian

  6. #5
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    Jul 1999
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    Glen Iris, Vic, Australia
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    Makita support:
    "Just use them once a month"

    Three other hardware stores
    "A month is fine"

    Local power tool repair shop:
    "4 weeks is fine. just charge them to full"

    Another local power tool shop:
    "4 weeks is fine, 6 months would be considered long term"
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  7. #6
    Join Date
    Feb 2006
    Location
    Perth
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    27,741

    Default

    don't want to just lock the trigger down on a drill to drain the battery.As I'm wary it will shorten the life of the drill.
    I doubt it would significantly shorten the life of the drill - it's not like it's under any load - that's what will affect bearings/gears etc and shorten the life of a drill.

    The table below from (BU-702: How to Store Batteries – Battery University) shows the percentages of remaining recoverable capacities of lithium- and nickel-based batteries after one year of storage at various temperatures.
    At 0ºC the difference between 40% and 100% charge is 4% for one year so for 4 weeks it would suggest you would lose ~0.33%
    At 25ºC the difference between 40% and 100 charge is 16% so over 4 weeks it should lose ~1.3%.

    This data is for Li-Co batteries, newer Li batteries may have improved performance.
    Screen Shot 2017-10-13 at 6.49.34 am.png
    What this shows is that storing Li-ion batteries in a hot shed is not a good idea.
    The same link above recommends a storage temperature of 15ºC for batteries.
    Presumably this takes into account that condensation inside batteries stored at lower temps can lead to probs.

    For 4-5 weeks I wouldn't worry about about it too much as the batteries have a finite life anyway.
    The 36V Li-ion battery for my mower sits in the charger on full charge for ~2 months at a time without being used during winter.
    This battery is >5 years old and I only just noticed it has a reduced capacity.

  8. #7
    Join Date
    Jan 2014
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    Sydney Upper North Shore
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    Having used NiCd up to LiPo batteries for model planes, it has always been explained to me that with these style of batteries, measuring the voltage is not a reliable method of assessing state of charge. The batteries tend to have very flat voltage planes as they discharge then drop off rapidly when they are nearly fully discharged. The Battery University has some interesting graphs re state of charge (SoC) re voltage and capacity and they state this;
    Each battery chemistry delivers its own unique discharge signature. While voltage-based SoC works reasonably well for a lead acid battery that has rested, the flat discharge curve of nickel- and lithium-based batteries renders the voltage method impracticable.”

  9. #8
    Join Date
    Feb 2006
    Location
    Perth
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    27,741

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    I have been thinking abut using one of these to tell me what mAh has been delivered by a USB battery.
    https://www.ebay.com/p/LCD-USB-Detec...d=311933685405
    Given the price (start at around US$3) it's a wonder these are not standard in all power tool batteries.

    The remaining working energy could be determined if one knows the total mAh capacity of the battery.
    However, given
    - I would not trust a manufacturers spec on this and
    - One never knows how long a battery has been in storage.
    A capacity test would be needed i.e. almost run one flat to measure real total mAh.
    Then again, the capacity changes with time and multiple tests to "almost flat" to recalibrate current working capacity are probably not a good idea.

  10. #9
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    Feb 2003
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    back in Alberta for a while
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    Quote Originally Posted by barrysumpter View Post
    Makita support:
    "Just use them once a month"

    Three other hardware stores
    "A month is fine"

    Local power tool repair shop:
    "4 weeks is fine. just charge them to full"

    Another local power tool shop:
    "4 weeks is fine, 6 months would be considered long term"
    fine

    but why do you have / need TEN 3 Ah batteries?
    Even when using 9.6V NiCads I could charge one battery in about the time it took to discharge the other. The small overlap was a good excuse to stop for a cuppa
    regards from Alberta, Canada

    ian

  11. #10
    Join Date
    Apr 2009
    Location
    Wollongong, Australia
    Posts
    131

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    Best way to look after Lithium batteries is to use a smart charger like the radio control hobby people use (especially the big RC helicopter people).
    I don't bother with my power tool batteries though - I just try to make sure when I put them away they have been used and are not on a full charge, and likewise are not totally empty.
    The smart chargers RC hobby people use can measure the capacity of the battery or allow you to enter it, and can charge and then discharge to storage level (or even fully discharge for disposal). They can also monitor the internal resistance of the battery over many cycles and give you an indication of the condition of the battery. They also ensure that all cells within a battery are balanced during charging. For heli LiPo batteries it is important not to store at full charge - people in the hobby have experimented with this and published data that shows the reduction in lifespan of battery is not insignificant if stored fully charged. These sort of chargers are expensive though if you don't have plenty of uses for them. This is a good place buy a smart charger from Chargers - ProgressiveRC
    I have an icharger 106B+ for my RC hobby needs - its a budget option but I would highly recommend it.
    If you know you aren't going to use the batteries for a while though and have no way to accurately discharge and are worried, best thing to do is store them in the fridge.

  12. #11
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    Jul 1999
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    Glen Iris, Vic, Australia
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    Thanks to all.
    Much appreciated!

    Storing them fully charged in a cool place out of the tool.
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  13. #12
    Join Date
    Dec 2010
    Location
    Melbourne
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    Default

    Do you have a radio or torch? If you know the full runtime of the devices then put a timer and let it go for half the runtime. That should be near 50% charge.

    It's very good idea to keep your batteries at 60-80% state of charge and store them in a cold place to slow down the chemical deterioration process. I keep all my lithium batteries in a bar fridge which I modified the thermostat to run at 15C. So it's not too cold that I have to thaw the battery if I need something quickly.

    I have been doing this for many years and lots of my older digital camera batteries are still functioning and stores healthy amount of charge.

    You should not fully topup the batteries if you are not planing to use it soon. Charge before use, rather than charge after use.

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