Battery Longterm Storage Strategy For Cordless Tool

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Hank33
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Battery Longterm Storage Strategy For Cordless Tool

I’ve got a Makita cordless screwdriver and 3 extra batteries. I hardly use the tool never mind the other 2 batteries lol. I was thinking of discharging the other 2 till 40%-60% for long term storage. Sound like a good idea?

 

                                                                                             

nocturne
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That is what is recommended for Li-ion storage, ~3.7V

flydiver
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Yes.
If it’s possible to easily yank the battery, I’d do that to prevent any occult parasitic drain.
Since it’s used seldom you might try to keep the working battery under 4.0v. It will still perform fine, have decent capacity, and be a little easier on the cell. Take it down to 80% if rarely and only lightly used.

To Air is Human, to Respire….Divine.

Hank33
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Ok great info! Now to find a block of wood, screws and then start screwing them in and out till I get the capacity down hehe.

 

                                                                                             

kennybobby
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There is a parasitic drain current inside the pack to keep power up to the BMS. i don’t know the time constant but it can unbalance the pack internally and cause it shut off the output FETs, which locks it up. Sometimes you can open the pack and recharge the depleted cell and get it to reset, but no guarantee this will work.

So the price of freedom and useful lifetime is regular periodic checking and charging.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

docware
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The best strategy is to keep them below 50% SOC, so below 3,7 V per cell. Low temperature is also very friendly factor for long term storage.
BMS drain is usually very low, about 30 μA. So that checking the battery every 6 – 8 month is sufficient enough.
Assuming that battery is Li-ion.

kennybobby
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In the ryobi packs the BMS chip Vcc pin is spec’d at 30-100uA in sleep mode, but it also other current drains, namely an internal 3.3V LDO regulator that draws 100uA, and an internal 10VLDO regulator at ≤ 10mA.

There is a PIC 16F microcontroller that is always ON and draws the 100uA from the BMS chip.

The 10V regulator supplies power to keep the charge and discharge FETs ON; one is driven from the PIC and the other from the BMS chip.

Without the source code we don’t know the time constant for powering down to sleep mode, or if it ever does, but even if it did there is still quite a bit of current draw that will drain a pack. i wouldn’t recommend to wait 6 months with a ryobi, it will be dead and ready to sell on ebay; ebay is covered up with dead ryobi packs for sale.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

d_t_a
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docware wrote:
The best strategy is to keep them below 50% SOC, so below 3,7 V per cell. Low temperature is also very friendly factor for long term storage.
BMS drain is usually very low, about 30 μA. So that checking the battery every 6 – 8 month is sufficient enough.
Assuming that battery is Li-ion.

!https://i.imgur.com/I8fS1r1.jpg!

That’s informative, docware. Would you be able to share the source/link of this study? Would like to read more about them.

docware
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d_t_a wrote:
That’s informative, docware. Would you be able to share the source/link of this study? Would like to read more about them.

Well, it is from study “Aging of Lithium-Ion Batteries in Electric Vehicles”, here is the link :

https://mediatum.ub.tum.de/doc/1355829/file.pdf

Look at page 50 – 52.

docware
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kennybobby wrote:
In the ryobi packs the BMS chip Vcc pin is spec’d at 30-100uA in sleep mode, but it also other current drains, namely an internal 3.3V LDO regulator that draws 100uA, and an internal 10VLDO regulator at ≤ 10mA.

You are right, each OEM has different specification depending on the electronic used in the equipment. So that initial checking should be earlier, maybe after 2 – 3 months.
Battery in my Bosch cordless screwdriver is relaxing below 50 % SOC for more than year without any issue.

docware
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Another interesting study “ Calendar Aging of Lithium-Ion Batteries “ is here :

https://iopscience.iop.org/article/10.1149/2.0411609jes/pdf

kennybobby
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Thank you very much for the document links.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

ZoomieFan
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At my parents place is a deWalt that’s not much used either.
Long story short, the battery that’s in the charger all year around still works great, the others are totally dead.

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

docware
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The old cordless tools had big problems with battery because of high self-discharge rate of NiCd cells. It is useful to know what cells are in my battery.

pennzy
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I find my cordless tool batteries do better when stored in the cold rather than warm.

kiriba-ru
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Can not agree some of the comments above.
First at all, in your area you should rather try to avoid too cold conditions. Holding batteries in living home area is perfect, no needs in any extra conditions like putting them in fridge. If you will need them ocationally for outside work in winter, you will have batteries that are ready for use (rc model builders like holding li-pos in fridge, but it takes time to warm them before real load).
Battery pack is not bare cell. It has some parasite drain and holding batteries that are not going to be used soon at full charge is more safe than holding them partly empty and meeting situation when brand charger wont be able to start them anymore.

pennzy
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When doing construction I keep my Dewalt tools in my van. Maybe just coincidence but all of my failed batteries came in the summer. Granted, frozen batteries need to warm to work at full capacity.