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  • Some Tech Advice Please

    I'm pretty well caught up on home repairs and unless something major happens my 18 volt nicads are gonna be sitting on a shelf all winter. In the past I've run down the battery in one of the tools in order to get a good charge. Please tell me the lowest safe voltage I can allow them to reach before charging? I don't want them to go completely dead and I'd rather not recharge them if they don't need it and build up the memory. I know this was mentioned previously but I neglected to write down the numbers. I plan on using my label maker to label the info right on the charger. Thank you.

  • #2
    Re: Some Tech Advice Please

    Since my shop is unheated I bring them in the house and let them set until needed. If they need charging I just charge and do the job. Mine are DeWalt and they do not recommend draining the battery all the way before charging. My chargers have a tune up mode on them and will tune the battery if left on for 8 hours. The big thing to long life is to not store them outside of the recommended operating temp range.
    SSG, U.S. Army
    Retired
    K.I.S.S., R.T.F.M.

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    • #3
      Re: Some Tech Advice Please

      Thanks for the reply. I've ruined a couple of Ryobi batteries by draining them too low. I remember someone posting an actual voltage number for the 18 volt nicad to reach before recharging. If that number is let's say 12 or 13, then I can occassionally check the batteries with my volt meter and when they drop down to that magic number I'll throw them in the charger. Thanks again.

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      • #4
        Re: Some Tech Advice Please

        Living in Arizona I really don't have to worry about the "cold".
        I do worry about excessive heat..we can hit 110F easily in the summer.

        I have the 18v nicad batteries. Some are the HC style and others are the 2.5AH style.
        I keep them in a cotton tool bag inside the house.

        I use those yellow 3-M sticky papers to label when the battery was last on the charger.
        I then rotate my batteries and use the older ones first.

        I have not had a battery fail and I started with these things back in late 2004.

        As far as leaving batteries alone for a long while, I try to visit them at least every 2-3 months if I'm not doing any significant project requiring their use.

        If a battery is three months old without use I'll pop it into the flashlight or a tool for a bit and then exercise them. finally I'll place them into the dual charger and let it do its thing. After the battery is charged I'll return it to the pile.


        Cactus Man

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        • #5
          Re: Some Tech Advice Please

          Cactus MAn, that's pretty much the way I've been handling things although I stopped running the batteries down with the flashlight. I ruined a couple of Ryobi 18's that way because they drained down too much. Lately I just run them down with the drill when they feel like they're getting weak. Thing is a couple of the guys posted specific voltage numbers of when to throw them in the charger. Since I'm getting more and more lazy, I figured instead of running the batteries down I'd just check the number they were at.Can't argue with your method, it's worked so far. If I don't get that technical number, I'll just keep do'in what I've been do'in. Sure will be nice when those Higher AH lithiums show up, no more play'in games.

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          • #6
            Re: Some Tech Advice Please

            First of all, the cold is unlikely to hurt the batteries. I know of some people who claim to freeze them. The general rule is to not let the individual cells get below .9 volts. That gives you a little factor of safety for uneven voltages. A 18 volt battery has 14 cells, so that is 13 volts. Also, you shouldn't worry too much about memory. You are unlikely to hurt it by topping it off every month.

            I am not good with maintenance this way. I too often forget about batteries for over a year and then they often don't come back to life. I've learned that if you refrigerate them they lose juice much slower. I only need to recharge them once a year and I've never had a battery die in the refrigerator.
            Last edited by Disaster; 11-29-2007, 03:59 PM.

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            • #7
              Re: Some Tech Advice Please

              Disaster, I really appreciate that detailed answer. I'm going to get out my label maker now so I don't get side tracked. I've heard about putting batteries in the fridge, but my wife would give me hard time about doing that. I thought topping them off would cause a problem and that's why I wanted to let them just discharge to a safe low voltage on their own. Thanks again.

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              • #8
                Re: Some Tech Advice Please

                Heat and overcharging probably kill nearly as many batteries as letting them go too low. Those chargers that trickle charge are generally a bad idea...especially if the battery feels warm to you all the time. I bought Radioshack AAA chargers, for their little RC cars. They claimed you could just leave the batteries in the chargers all the time. Most of them died in less than a year following that recommendation. Having said that, leaving them on a charger is an entirely different thing than just running them through a charge cycle (as long as you don't forget about them and don't leave them on the charger.) On any decent charger you shouldn't hurt your batteries, topping them off every few months....just take them off the charger as soon as the cycle is done.

                P.S. There are some stupid chargers that charge based on time...the same amount no matter what condition the battery is in. These can be really rough on batteries...especially if you just top off. There are also cheap tool batteries that only trickle charge...taking 10-15 hours to fully charge a battery. With these you should reduce the time if you are topping off. The Ridgid chargers, and most better chargers will turn off based on heat (or voltage.)

                I keep my RC batteries in the basement, where it is cool (too many for the fridge) and recharge them about every 6 months...but sometimes every year. Luckily we have a second, old 'fridge, that my wife lets me use one small area for batteries. I keep the expensive ones there...like the tool batteries.
                Last edited by Disaster; 11-29-2007, 06:46 AM.

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                • #9
                  Re: Some Tech Advice Please

                  When you discharge you want to take them down to 0.9v per cell. So for an 18v drill that's 15 cells X .9v = 13.5v

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                  • #10
                    Re: Some Tech Advice Please

                    Originally posted by GilBeQuick View Post
                    When you discharge you want to take them down to 0.9v per cell. So for an 18v drill that's 15 cells X .9v = 13.5v
                    Jeesh...I was wayyyy off....not sure what I was thinking or drinking when I posted that. Thanks for jumping in and correcting me, Gil. It is generally considered to be safe to go to .9-1.0 volt per cell. I will correct my post.

                    Gil probably hasn't taken apart a pack lately so he didn't realize manufacturers short higher voltage packs by a cell. You would expect, given the nominal voltage of 1.2v per cell that an 18v would have 15 batteries (1.2x15=18) but somewhere between 14.4v and 18v manufacturers started "cheating" consumers out of a battery cell.

                    The correct safety range is 12.6 to 14 volts for an 18 volt pack.

                    P.S. Here is a nice little article on NiCads.

                    http://www.repairfaq.org/ELE/F_NiCd_Battery.html

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                    • #11
                      Re: Some Tech Advice Please

                      Thanks for the correction guys, no harm done. The only batteries I routinely top off are my AA and AAA NIMH, about every two to three weeks, they seem to lose fast. Thanks again for the updated information.

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                      • #12
                        Re: Some Tech Advice Please

                        If you are topping them off that often they probably aren't very healthy. I highly recommend the GE/Sanyo Eneloop batteries. You can buy a set with 8 AA's and 4AAA's and a charger from Costco for $27. The Eneloops have are a new NiMh technology that has a very slow self discharge rate....on the order of 30% per year. These are the first rechargeables that you can use in slow drain applications like remote controls.

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                        • #13
                          Re: Some Tech Advice Please

                          Second that Eneloop recommendation. I use them in my thirsty TV remote.

                          All due respect though Disaster, Radio Shack anything is no basis for assessment of anything. I do electric vehicles for hobby (not RC, but actual vehicles). I try not to think about NiCad technology, but with LiIon ther's alot to be said for leaving the battery on overnight to trickle-charge. It tops it off and gives you the best long-term use, although we do have lifetime warranty. All but the cheepest LiIon chargers cut back based on battery temperature, and otherwise condition the batteries for long life and no explosions. Just don't short those terminals!

                          For long-term storage, LiIon should be stored in the fridge at ~40-60% charge.

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                          • #14
                            Re: Some Tech Advice Please

                            Originally posted by Quantum View Post
                            For long-term storage, LiIon should be stored in the fridge at ~40-60% charge.

                            Here's a chart that gives you the estimate capacity loss for lithium ion at different temperatures/charge levels:
                            http://www.batteryuniversity.com/parttwo-34.htm

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