Battery Charger Questions

[MiamiCuse]

I have a cordless drill using NiCad bateries. They died a few weeks ago and last week I got two new batteries.

I fully charged one, used it and waited till it was fully drained, and started charging again...STUPID ME, I forgotten about it and left it in the charger for a full week and didn't realized it until today!!!

I heard that if you left your battery in the charger after it has been fully charged it will create the memory effect again, is this right? Did I ruin this new battery by my dumbness again?

One other related question, my cell phone uses a lithium ion battery. I have a car charger and a regular charger. My friend told me I should avoid charging with the car charger as much as possible because they create memory effect on the battery. Is this true? I could not find any online references for this.

Thanks in advance,

MC

[JIMMIE]

Neither case has ever happened to me. I leave the batteries for my drill in the charger continuously until the next time I need it. Never had a problem but I must admit after 4 years they dont hold up quite as good as they used to. Is this memory?

Jimmie

[ransley]

You say you fully discharged it, well that can kill Nicads by causing cells to reverse polarity, you left it in a charger a week, most new chargers stop charging when the cell peaks. Was the battery real warm, if not I would not worry about the charger continuing to burn it up but a nicad is fully discharged when the drill just slows down, drain them dead will shorten its life, so will overcharging.

[Angello Huong]

Fully discharging the battery probably drastically reduced the number of recharge cycles that you can get out of it--in the long run.

About the leaving the battery on the charger question: It depends on whether the charge is voltage regulated or not. Some chargers switch to trickle charge after a certain voltage level is hit. The cheaper ones usually don't and they keep loading up the battery with electricity that the battery can't take in after its been fully recharged. That will kill a battery life as well--either by shortening the battery liftspan due to the excess energy being converted into heat or maybe altering the chemical balance of the battery acid & fluids.

Check the power output specs on the back of the AC box. It should list output voltage and the amps that is generates. The voltage output should only be about 5-10% or so more than the battery rating (i.e. 12.6-13.2V output for a 12V battery). And the amperage should only be 1/30th of the battery's capacity (i.e. 0.1 amps output for a 3 amp battery). That's the level for a safe trickle charge.

Just a general rough estimate based on my experiences in owning a couple dozen different rechargeable gadgets over the years.

[Stormin Mormon]

From what I've heard over the years the nicad "memory effect" is that repeated shallow, partial discharges, and that some how limits future discharges. Different people say that is real, or not real. I've not had that problem.

Some chargers will dry up the cells due to electrolysis, but no way to know if your charger does that.

I've not heard of lithium cells having memory effect.

I think you're worrying about tiny stuff, and you are wasting your worry power.

[Stormin Mormon]

That's something called "expected lifespan".

[SMS]

Some of the cheaper drills have chargers that don't cut off automatically when charging is complete and the instructions warn you to not leave the drill on the charger continuously. One week probably did not destroy the NiCad batteries.

In any case overcharging causes voltage depression, not "memory effect." Every time you overcharge (never leave the batteries on the charger continuously) you damage the battery a little. You didn't destroy them with one week of overcharging, you just damaged them a tiny bit.

While you don't want to leave them on the charger continuously, nor do you want to let them self-discharge after long periods of non-use, which is worse than occasional over-charging.

If you only use the tools occasionally, hook the chargers to a timed outlet, and charge them for an hour every week, using a timer like the Intermatic DT620CL. Unfortunately some charges require that you push a button to initiate charging (these tend to be the charges with a micro-controller that monitors charge state and turns the charger off when the batteries are charged, but it doesn't turn it back on as the batteries self-discharge).

Your friend has no idea what he's talking about.

[Oren]

The OP has one un-used new battery. How long can it sit on the shelf, before any potential damage?

Anyone?

[Ed Pawlowski]

Not sure, but they do lose charge over time. I plug them in every month or so to keep them topped up. In two months they are near dead otherwise.

[MiamiCuse]

I bought them new, but they may have already sat on the shelf for months, right?

[Stormin Mormon]

A very old memory, here. Nicads used to be shipped some how factory discharged. You'd have to leave em on charge for a full day, and then use them. They shelf life for many years, with the factory "setting".

[Tony Hwang]

Hi, Key is using a smart charger.

[Van Chocstraw]

No

No

[SteveB]

Most all battery chargers have a light on it that indicates charging status. Do you think that if it takes 8 hours to charge a battery that the battery using public will put it on a charger, and then stay up for eight hours until the wee hours in the morning to shut it off? No. They have an automatic shutoff that will stop charging when it gets fully charged. Same with cell phones.

Think about it. If this was a big problem, we would have heard all about it by now with exploding batteries or burning houses.

Yes, NiCd are bad about memories. But the thing that causes memory problems is if you partially discharge it, and then charge it, that is where it develops memory. I have used a rubber band on the trigger to keep it on and drain the battery completely. Use the thing until it just won't turn a screw or even turn with your hand holding the chuck, you want it to be that weak. And next time, buy a NiMh battery drill, which you can recharge at any state of depletion with no memory effects.

If you have doubts, call the cell phone provider and see if your phone is one that needs special treatment.

I'd say no.

Steve