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,
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?
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.
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.
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.
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
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".
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.
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