Ryobi Battery Charger?


Is there any problem with leaving the Ryobi 18v batteries in the charger for days/weeks/months after the green light comes on? In the past I have removed them soon after the green light comes on, indicating fully charged; it later appears that after days or weeks much of the charge has been lost.
Enlightenment appreciated.
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CWLee
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What I have noticed is my 2 ryobi chargers overcharge my pack going by the temp method of charge, a nicad battery is fully charged just when temp increases so I take out my pack when its done by the green light, my sony and sanyo charger dont do this to ryobis extreme of heating a pack, I dont know if it continues to charge or at what voltage if it does, but a warm pack of near 80f is full to overcharged, and I dont know how much of the heat is the charger itself but what I see is it overcharges packs all the time. A 1.2v nicad is discharged at 1.2v and fully charged at 1.33v or so, you would need to check voltage and temp to figure out if ryobi is keeping it overcharged or cycling, or nothing at all since its supposed to be a smart charger. Overcharging cooks a battery into shorter life, overdischarging is not good either. My ryobi packs dont hold a charge either so I dont think they are top grade Sanyo or Panasonic cells, but you dont pay top price either. Companies make big money selling replacement bateries so I dont trust chargers to be designed for longest battery life.
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ransley wrote:

A nicad is approximately 80% charged when the temperature starts to increase; this is also about when the voltage starts to decrease. In contrast, NiMH don't start to heat until about 100% charge, at which time their voltage flattens or decreases very, very slightly. And it's normal or the temperature to rise 20F.

Voltage isn't accurate enough to indicate full charge, and 1.33V is too low. Instead chargers use rate of voltage change (or even the rate of rate of change), temperature, or rate of temperature change. Charging to just 80% of capacity will make NiMH and nicad batteries last longer, but I doubt that's done except for ultra-high reliability equipment (space) or hybrid cars. Some chargers follow the full charge with a lower current top-off charge that can add 10% more capacity
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NiCd batteries have an inherent self-discharge rate,something like 5% per day. Some chargers may slowly discharge a pack if left in. I suspect the cheaper brands may be that way.
Perhaps the Ryobi website has a FAQ?
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Jim Yanik
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Perhaps it does, but I could not find it.
Thanks for your other comments as well.
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How long does it take for the self-discharge to discharge them when you are unhappy. After a couple of weeks, they will lose enuf that it will be noticeable if they are NiCAds. You should give them a little jolt every couple of weeks if you want them to not disappoint when you really need them if they are NiCads. Nickel metal hydrides are not as bad, LI cells are the best.
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I don't know how long it takes. I only make use of these cordless tools on a random basis. When something breaks that requires drilling or cutting I put one of the batteries into the tool and go to work. I can only get about 15 minutes of sawing or drilling before there is a noticeable weakness. Then I put the battery in use on the charger, use the spare until it gives out, and sometimes I've finished the project by then; if not, I take a break until the green light comes on showing fully charged. Then I can saw and drill much longer - I don't know because I've never reached that maximum usage level with a freshly charged battery.
Thanks for your comments.
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wrote

with your type of intermittent usage,you need tools that use the Lithium ion batteries. They retain something like 80% charge after 6 months.
I would also select tools that come with a 1 hour charger. My old Makita 6095 uses 9.6V sticks,and they charge in a hour,so I recharge them before starting a job.Makita sells some cordless tools with lithium packs,but they are not inexpensive.Black& decker sells some lower cost Li- ion tools.
ISTR that Ryobi chargers take 3-5 hrs or even overnight.
Maybe they sell Li-ion packs for your present tool,but you'd likely need a new charger,too.
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CWLee wrote:

It shouldn't hurt, provided it's not done it regularly. Most batteries fail when a cell overcharges and grows a crystalline whisker long enough to short adjacent plates. Some people apply high current at 12-100V DC to that cell alone to vaporize the whisker, but it usually grows back in a day or week. Chargers are designed to sense full charge and either shut down completely or go into maintenance mode where slow low current pulses are sent out. The pulsation is intended to cause whiskers to break up before they grow too long, but it doesn't seem entirely successful.
Sometimes a cell doesn't short but merely goes into reverse polarity, and that can be cured by applying low current directly to that cell for a minute and then immediately charging the whole battery normally. This can be done with an ordinary 1.5V alkaline cell connected to the affected nicad through a 10 ohm resistor (+ terminal to + terminal; tie negative terminals directly together)
It's normal for batteries to warm up when they reach full charge. Nicads start warming at approximately 80% full charge, NiMHs at about 100%.
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