10.8V Lithium Battery question

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  • leehljp
    Just me
    • Dec 2002
    • 8429
    • Tunica, MS
    • BT3000/3100

    10.8V Lithium Battery question

    I have a 13-14 year old 10.8v Hitachi right angle cordless impact driver that I use on occasion that is similar in function to this:
    https://www.amazon.com/Makita-XLT01Z...9565193&sr=8-3

    My Hitachi of course has been discontinued and so has the battery (from Hitachi). I have found replacement batteries on eBay, and also offered is the same shape/physical size in 12V size. Same physical components to fit my Hitachi.
    QUESTION: can the 12 volt battery work safely on the 10.8V tool? The question is about the voltage, not about the physical shape or size. It seems that I have heard of people doing this off and on.

    I don't use this tool often but when I need it, there is nothing that works like it does. I can drill with the impact driver easily enough with hex head drill bits (and I have a full set in 16ths up to 3/8) and as an impact driver, it does screws easily enough in tight situations. I have been wiring our kitchen for under the counter lights and it fits easily into places where a drill will not. The current lithium battery goes for about 20 minutes of actual work before stopping, about a third of what it used to do. But 20 minutes of actual work spread across drilling and screwing in screws is about 3 hours for me.

    Curious: ANY IDEA if the 10.8v charger will charge the 12V batteries? It is a Lithium charger.

    Thanks

    I FOUND THE ANSWER BY GOOGLING 10.8V VS 12V. They are basically the same. In general - Internationally, they are listed as 10.8v while in the USA they are listed as 12v.

    Your insights are still appreciated.
    Last edited by leehljp; 08-21-2021, 12:51 PM.
    Hank Lee

    Experience is what you get when you don't get what you wanted!
  • mpc
    Senior Member
    • Feb 2005
    • 979
    • Cypress, CA, USA.
    • BT3000 orig 13amp model

    #2
    Most rechargeable batteries output less and less voltage as they are drained/used. So, when fully charged, the voltage is at its peak value. It drops a few tenths of a volt rather quickly, with just a little use. Then it ramps far more slowly with more and more use - for all intents and purposes, this is the "real working voltage" of the battery. Battery makers average the voltage over this region for the cell rating. Once the battery charge is nearly used up, the voltage begins to drop quickly again. Modern batteries and cordless devices will detect this latter drop-of and cut off the tool to prevent excessive battery discharge. In fact, most batteries have the over-charge and over-discharge cutoff circuitry built into the battery case. Batteries intended for radio controlled airplanes/devices often omit this protection circuitry - so the propeller doesn't just stop in the sky!

    Click image for larger version  Name:	image002.gif Views:	0 Size:	7.3 KB ID:	844953
    The overall shape of this curve depends on how much current is drawn from the battery too - i.e. how quickly one tries to discharge it. A slow discharge rate will flatten the center portion a bit; drawing current more rapidly than the battery was designed for makes the initial fall-off larger and makes the voltage "cliff" happen around 80% instead of 90%.

    For the early lithium-ion cell chemicals, the 100% charge voltage is about 4.1 volts so 3 cells results in just over 12 volts output. The "real working voltage" is around 3.6 volts so 3 battery cells outputs an average of 10.8 volts. Hence the two different ratings depending on who is doing the marketing. It reminds me of the "5 Horsepower Peak" ratings of shop vacuums... no way a standard 120 volt/15 amp outlet can provide that kind of energy for more than a split second before the circuit breaker trips.

    The more recent lithium-ion cell chemical formulas spit out 4.2 and 3.7 volts. An older charger would probably work okay on them. Using a charger for modern lithium-ion cells on the original/older cells might be risky: you do not want to overcharge (or over-volt) batteries during charging especially lithium-ion. Under-volt chargers are safe; they may not bring a new style battery to 100% charge however.

    For your driver tool: what is the amp-hour rating of the original battery pack and the potential replacement? If the replacement pack rating is equal to or larger than the original rating then I would expect satisfactory performance. If the replacement pack has a lower amp-hour rating, your tool may draw more amperage (more current) than the batteries were designed for. They'll work... but the amount of time you get out of the tool between charges will be less and the batteries will age faster too. How "fast" is your charger? Normally, the charge rate is similar to the battery's designed discharge rate or smaller; trying to "fast charge" a battery creates a lot more heat. Does the replacement cell pack include at least as many cooling vent holes as the original battery pack?

    mpc
    Last edited by mpc; 08-21-2021, 04:01 PM.

    Comment

    • LCHIEN
      Internet Fact Checker
      • Dec 2002
      • 20914
      • Katy, TX, USA.
      • BT3000 vintage 1999

      #3
      MPC posted a chart of discharge curve of Lithium ion batteries. Saves me the trouble. As you can see, it holds voltages as high as 4 when just charged and then drops to 3.7 and 3.6.
      So you can have a wide range of voltage for three cells... 12 to 11.1 and 10.8 and places in between.
      So you see all kinds of labels for the battery packs when they are really all the same.

      What I would personally recommend is to take it to a place like Batteries plus or similar. and avail yourself of their battery rebuild services if you give them an old pack.
      It saves shipping costs of a heavy pack which can amount to $20 both ways (making it much cheaper than on-line mailed in shops) and they will do it properly with the electro-welded steel straps between fresh new batteries. Something you don't have access to DIY.

      Pretty much you can call a battery pack whatever you want... my Craftsman 19.2 V series started out as NiCd or NiMh with like 15 cells rated 1.25 volts per cell.
      When they upgraded to Lithium batteries and chargers for the same tools, they used 5 Lithium cells which make 19.2 when they have about 3.8.volts.
      So really electric motors are OK with +/-10% at least on the voltage... or they should be designed that way because batteries are just not a flat voltage, the voltage always has some decline during the discharge life.
      Electronics, too. Four AA battery electronics are nominally 6 volts. But they are designed to operate to 4. to 4.4 as the end of useful battery life.
      Beause ALaklines decline from 1.6 to 1 to 1.1 where they just give out totally, and AA NiCd and NiMH start out 1.35 fully charged but drop to 1.2 very fast and peter out completely at 1 to 1.1 volts per cell.
      So a four battery electronics item can usually be counted to work with 4 to 4.4 starting all the way to 7+ volts as a matter of good design.
      Last edited by LCHIEN; 08-21-2021, 07:54 PM.
      Loring in Katy, TX USA
      If your only tool is a hammer, you tend to treat all problems as if they were nails.
      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

      Comment

      • leehljp
        Just me
        • Dec 2002
        • 8429
        • Tunica, MS
        • BT3000/3100

        #4
        Originally posted by mpc
        For your driver tool: what is the amp-hour rating of the original battery pack and the potential replacement? If the replacement pack rating is equal to or larger than the original rating then I would expect satisfactory performance. If the replacement pack has a lower amp-hour rating, your tool may draw more amperage (more current) than the batteries were designed for. They'll work... but the amount of time you get out of the tool between charges will be less and the batteries will age faster too. How "fast" is your charger? Normally, the charge rate is similar to the battery's designed discharge rate or smaller; trying to "fast charge" a battery creates a lot more heat. Does the replacement cell pack include at least as many cooling vent holes as the original battery pack?

        mpc
        Edit: the Original 2500mAh. it doesn't have this on the battery but I did some digging and think the original was/is 2500mAh.
        New ones are the 3000mAh or 4000mAh.

        "Does the replacement cell pack include at least as many cooling vent holes as the original battery pack?": I'm not sure but as far as I can tell by the picts, it looks identical to the OEM.

        Thanks. I am going to order one through eBay for $19.99.
        Last edited by leehljp; 08-21-2021, 09:40 PM.
        Hank Lee

        Experience is what you get when you don't get what you wanted!

        Comment

        • leehljp
          Just me
          • Dec 2002
          • 8429
          • Tunica, MS
          • BT3000/3100

          #5
          Originally posted by LCHIEN

          What I would personally recommend is to take it to a place like Batteries plus or similar. and avail yourself of their battery rebuild services if you give them an old pack.
          It saves shipping costs of a heavy pack which can amount to $20 both ways (making it much cheaper than on-line mailed in shops) and they will do it properly with the electro-welded steel straps between fresh new batteries. Something you don't have access to DIY.
          WE have a Batteries Plus near by, and I have been in several times over the last 10 years. I have not been impressed with their work or knowledge. I think it is a local issue.
          Hank Lee

          Experience is what you get when you don't get what you wanted!

          Comment

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