Question on recharging NIMH batteries

Archived from groups: rec.photo.digital (More info?)

MB_ wrote:
> We use NIMH batteries in our Canon A75 digital camera. They work fine and I
> normally recharge them when they are just about out of charge.
>
> But, we are going on vacation soon. I would guess that the current batteries
> are maybe half-charged. Can I just charge them up now, or would this shorten
> the ultimate battery life?
>
> MB

Hi MB...

NiMh's don't suffer from the dreaded memory effect as the
nicd's did. They do however have a bit of a problem with
self discharge.

So, go ahead and charge them up, no matter the state of charge
when you start. Do it as close as reasonably possible to
your leaving date.

Take care.

Ken

Archived from groups: rec.photo.digital (More info?)

MB_ wrote:
> We use NIMH batteries in our Canon A75 digital camera. They work fine and I
> normally recharge them when they are just about out of charge.
>
> But, we are going on vacation soon. I would guess that the current batteries
> are maybe half-charged. Can I just charge them up now, or would this shorten
> the ultimate battery life?
>
> MB
>
>

The charger that I just bought, RECOMMENDS topping off batteries that
have partially discharged from lack of use.
My charger also has a "refresh " button which the manufacturer
recommends I use about every tenth charge. The refresh feature
discharges the batteries according to a set protocol and then fully
charges them.
Bob Williams

Archived from groups: rec.photo.digital (More info?)

NiMH batteries don't suffer from 'memory' reputed of NiCad. NiCads do
also get damaged from leaving in chargers too long and overheating, or
if the charger is a cheap charger that does not go into a pulsed
trickle mode after bring batteries up to charge, and the batteries are
left in them for very extended period. But NiCads have 1000+
discharge/charge cycles, whereas Li-ion and NiMH have about 300+
discharge/charge cycles in them. 'Topping up' NiMH won't hurt them,
per se, but may count against the 300+ cycle total. I have been using
NiMH batteries for a home entertainment remote control unit for close
to 5 years, and the two sets of batteries I maintain for this are
charged about once every other month (use set A one month, pull out for
charging and use set B the next month, etc) and batteries are still
going strong.

Archived from groups: rec.photo.digital (More info?)

On Sun, 20 Feb 2005 11:04:27 -0800, Bob Williams <mytbobnospam@cox.net>
wrote:

>MB_ wrote:
>> We use NIMH batteries in our Canon A75 digital camera. They work fine and I
>> normally recharge them when they are just about out of charge.
>>
>> But, we are going on vacation soon. I would guess that the current batteries
>> are maybe half-charged. Can I just charge them up now, or would this shorten
>> the ultimate battery life?

*Occasionally* charging batteries from half-full is very unlikely to do
any harm to any battery. Memory effects can bite if you do it regularly,
at least for some types.

>The charger that I just bought, RECOMMENDS topping off batteries that
>have partially discharged from lack of use.
>My charger also has a "refresh " button which the manufacturer
>recommends I use about every tenth charge. The refresh feature
>discharges the batteries according to a set protocol and then fully
>charges them.

The general opinion around these parts seems to be that full discharge
is necessary for NiCad batteries, but not NiMH. I'd certainly like to
know whether it's really necessary or not. Anyone got a definitive (i.e.
based on laboratory research) answer?

--
Stephen Poley

Archived from groups: rec.photo.digital (More info?)

"Stephen Poley" <sbpoleySpicedHamTrap@xs4all.nl> wrote in message
news:futh11hdppkb62n3ah352scfjufnkl5aff@4ax.com...
> On Sun, 20 Feb 2005 11:04:27 -0800, Bob Williams <mytbobnospam@cox.net>
> wrote:
>
>>MB_ wrote:
>>> We use NIMH batteries in our Canon A75 digital camera. They work fine
>>> and I
>>> normally recharge them when they are just about out of charge.
>>>
>>> But, we are going on vacation soon. I would guess that the current
>>> batteries
>>> are maybe half-charged. Can I just charge them up now, or would this
>>> shorten
>>> the ultimate battery life?
>
> *Occasionally* charging batteries from half-full is very unlikely to do
> any harm to any battery. Memory effects can bite if you do it regularly,
> at least for some types.
>
>>The charger that I just bought, RECOMMENDS topping off batteries that
>>have partially discharged from lack of use.
>>My charger also has a "refresh " button which the manufacturer
>>recommends I use about every tenth charge. The refresh feature
>>discharges the batteries according to a set protocol and then fully
>>charges them.
>
> The general opinion around these parts seems to be that full discharge
> is necessary for NiCad batteries, but not NiMH. I'd certainly like to
> know whether it's really necessary or not. Anyone got a definitive (i.e.
> based on laboratory research) answer?
>
> --
> Stephen Poley

NiMH batteries do like some exercise, so it's not a bad idea to discharge
them now and then, but it's not necessary as it was with NiCad's. I
wouldn't worry about it too much, as it doesn't take many uses before the
batteries pay for themselves. At some point they will need to be replaced.

BTW, these problems also have a lot to do with your charger. Some chargers
can read the state of charge in the battery and only charge it as much as it
needs. Others simply give the battery a given amount of charge for a
specific period of time. In other words, you put a partially discharged
battery in one of these cheaper chargers and it will "overcharge" the
battery, thereby shortening its life. Often it's overcharging and heat that
shortens a battery's life. Also, some chargers might take 4 batteries, but
charge them in pairs, not individually. So, you put in one battery that's
fully discharged, and one that charged, and it will charge them both fully,
again, shortening the life of one of the batteries. So, don't forget about
the quality of your charger. It's just as important, if not more important
to the overall health of your batteries.

In a decent charger you should be able to put in 4 batteries, each at a
different level of charge, and the charger will charge each individually.
Once charged, you should be able to leave the batteries in the charger
indefinitely, since it should drop to a very low trickle charge, although
it's best to take them out. We don't want to burn the house down, just in
case.

That's everything I know about batteries.

Archived from groups: rec.photo.digital (More info?)

Thanks for your interesting responses.
But, one comment. With a charge/discharge cycle of say 300, these batteries
will last MANY years in my digital camera.

So, it seems no big deal --- they will certainly be cost effective!!!

Mel


"Paul Busby" <me@privacy.net> wrote in message
news:37sn36F5disc7U1@individual.net...
> Thus spake MB_:
>> We use NIMH batteries in our Canon A75 digital camera. They work fine
>> and I normally recharge them when they are just about out of charge.
>>
>> But, we are going on vacation soon. I would guess that the current
>> batteries are maybe half-charged. Can I just charge them up now, or
>> would this shorten the ultimate battery life?
>>
>> MB
>
> The ideal storage capacity for most types of battery is 40% but don't ask
> how you tell!
>
> After a heated discussion on whether or not Li ion batteries were damaged
> by allowing them to be nearly discharged, I read up on "secondary"
> batteries in general (some of it from the battery university link imnsysop
> mentions). It changed my view that NiMH were definitely superior to
> NiCads. Well, it seems in many respects that the main advantage is the
> lack of cadmium (which is supposedly in tiny quantities anyhow). I've
> always thought that NiCads self-discharge rate was bad but NiMH are even
> worse! They also can't take so many recharge cycles, they are however
> /less/ prone to memory effects but when they do succumb, there's little
> that can be do done but NiCads can be reconditioned by carefully
> controlled heavy recharging. The greater energy density of NiMH is
> probably their greatest attraction. The last time I checked AA NiMH were
> up to 2.5A/hr. NiMH do benefit from occasional deepish discharge but not
> nearly as much as NiCads need. NiCads also deliver a more linear power
> output before recharging is needed but I've digressed enough as it is.
>
> --
> Thank people in advance? Thanking or cursing them afterwards at least
> gives some feedback!
>

Archived from groups: rec.photo.digital (More info?)

> Thanks for your interesting responses.
> But, one comment. With a charge/discharge cycle of say 300, these
> batteries will last MANY years in my digital camera.
>
> So, it seems no big deal --- they will certainly be cost effective!!!
>
> Mel

Maybe... or maybe not. I've had widely varying lifespans on NiMH batteries,
and, after reading a bit more about them, find that some manufacturers talk
about durability in terms of damage if they fall to the ground. I don't
think that's something we normally think about with a battery; we assume
that it's this solid thing that isn't going to be negatively impacted by
dropping, but my own experiences suggest that yes, it's true, batteries
*can* be damaged by impact with the ground.

Curiously though, I've seen no testing done on this issue.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

Archived from groups: rec.photo.digital (More info?)

On Sun, 20 Feb 2005 12:26:18 -0500, "MB_" <mel@prodigy.invalid.net>
wrote:

>We use NIMH batteries in our Canon A75 digital camera. They work fine and I
>normally recharge them when they are just about out of charge.
>
>But, we are going on vacation soon. I would guess that the current batteries
>are maybe half-charged. Can I just charge them up now, or would this shorten
>the ultimate battery life?


Charging NiMH batteries before they are drained is not an issue
(unlike NiCads); go for it.