Can I substitute a NiMH battery for NiCd in a cordless phone?

[[email protected]]

I recently bought a cordless phone, which came with a NiCd battery. In the
manual it says:

"To reduce the risk of fire, use only 3.6V 850mAh Nickel
Cadmium (Ni-Cad) cordless telephone replacement
battery pack."

I've heard about the dreaded "memory effect" with NiCd batteries, so I'm
interested in replacing it with a NiMH one. Someone who is selling a 3.6V
1000mAH NiMH battery on Ebay claims it works with my phone, but will it really
be safe? Wouldn't want to install a NiMH battery and have the house burn
down.

 

[CWatters]

I recently bought a cordless phone, which came with a NiCd battery. In the
manual it says:

"To reduce the risk of fire, use only 3.6V 850mAh Nickel
Cadmium (Ni-Cad) cordless telephone replacement
battery pack."

I thought most phones came with NiMH cells these days for environmental
reasons.

I've heard about the dreaded "memory effect" with NiCd batteries, so I'm
interested in replacing it with a NiMH one.

The memory effect is much misunderstood and isn't the most likely cause of
cells failing to perform as expected.

Memory effect was first noticed in early satellite batteries that were
subject to many IDENTICAL charge and discharge cycles as the satellites
orbited the earth. When the cells were asked to discharge a bit more than
usual the voltage fell more than expected. This happened at the point at
which it would normally have been recharged.

In a phone the most likely cause of failure is long term overcharge. Once
the battery is fully charged most phone chargers switch over to a
maintenance charge program. This is designed to keep the cells topped up
because all cells "self discharge". Problems occur if the chargers over
estimate the self discharge rate. In fact dumb chargers have to use a
slightly high maintenance charge rate to allow for the variation between
different cell batches, temperature effects and aging. NiMH have a higher
self-discharge rate but not everyone sees this. They are also less tollerant
to long term overcharge.

Personally I always prefer to buy products that use loose AA size cells
rather than an assembled battery pack. That way if the manufacture has gone
bust you can still replace the battery.

 

[JM]

quoting:

NiCd is actually better in this use - it does not have problems with
sustained overcharging, which most phones do.
NiMH may do.

Ready made NiMh cordless batteries have cells that are spec'd for this kind
of service. It is in my experience that the NiCad packs are not
generally spec'd in the same way, so actually the NiMh packs are far better.

 

[L]

It says to charge them for 24h ...

The Panasonic replacement battery costs as much as a new phone .. so i
said "my ass" and found this cheap NiMH pack in a supply store for $4


Matt

 

[L]

My NiCd's suffer from all known battery abuse


Thanks all for the replies. I will go ahead and install the NiMH's

Matt

 

[[email protected]]

NiCd is actually better in this use - it does not have problems with sustained
overcharging, which most phones do.

Interesting, both you and CWatters mention that NiCd batteries handle
overcharging better than NiMH. Maybe I'll stick with the NiCd battery.

NiMH may do.
How long does it say to charge it before use?

12 hours.

If it's under an hour, then there may be a actual risk of moderate
overheating.
If it's over that, then in practice, there is no fire risk.

Good to know.

Thanks, everyone.

 

[[email protected]]

quoting:

Ready made NiMh cordless batteries have cells that are spec'd for this kind
of service. It is in my experience that the NiCad packs are not
generally spec'd in the same way,

Interesting, the NiCd battery that *comes with* the phone isn't designed to
handle the phone's charger?

so actually the NiMh packs are far better.

I will take this into consideration, thanks.

 

[PeteS]

The problem lies in the charging. NiMh and Nicads are similar, but not
the same, and NiMh in particular has unfortunate side effects if not
controlled properly during charge (like smoking).

Look at websites devoted to battery chargers (TI, Maxim, Linear Tech)
and you'll find each has its own charge techniques. Having implemented
chargers for both those (and others, such as Li-Poly and Li+), I can
assure you there are differences and you have to be really careful.

Cheers

PeteS

 

[Ted Edwards]

I recently bought a cordless phone, which came with a NiCd battery. In the
manual it says:

I also recently bought a cordless phone that came with a shrink erapped
3-AA cell NiCd battery. The phone would last for about 3 days of zero
to minimal use before the battery went dead. I picked up an identical
shaperd 3-AA NiMH pack at Walmart and substituted that.

Now, the charger was designed to charge the 650mah NiCd pack at about
C/10 so the charge rate for the 1300mah NiMH pack is only C/20 and is
most unlikely to harm it. 1300mah is pretty low for NiMH AA's but the
phone now runs for well over a week so we shall see.

Ted

 

[CWatters]

| In a phone the most likely cause of failure is long term overcharge. Once
| the battery is fully charged most phone chargers switch over to a
| maintenance charge program.

In my experience, most cordless phones don't switch over at all --
they just charge at a C/10 rate or so forever. So yes, it's long term
overcharge. Maybe the better quality ones do better, but I've never
seen one.

I have a six year old DECT system and this appears to switch rates.
Initially it charges at a constant rate then presumably when the cells ar
full it switches on and off roughly every 15-20 mins. The NiCad batteries
last about 18 months then we notice they either get hotter and hotter while
on charge or their capacity seems degraded.

 

[JM]

quoting:

Interesting, the NiCd battery that *comes with* the phone isn't designed to
handle the phone's charger?

Yes, that's generally what I see in the original NiCad batteries that come
with phones AND replacement NiCad's.

 

[JM]

quoting:

I also recently bought a cordless phone that came with a shrink erapped
3-AA cell NiCd battery. The phone would last for about 3 days of zero
to minimal use before the battery went dead. I picked up an identical
shaperd 3-AA NiMH pack at Walmart and substituted that.

Now, the charger was designed to charge the 650mah NiCd pack at about
C/10 so the charge rate for the 1300mah NiMH pack is only C/20 and is
most unlikely to harm it. 1300mah is pretty low for NiMH AA's but the
phone now runs for well over a week so we shall see.

Ted

But remember the cells used to make the NiMh pack are spec'd for continuous
slow charge so even slightly higher charge rates won't harm the battery.

These cells have the capability to recycle excess gassing back to the
electrolyte (up to a cirtain point), rather than overcharge damage the
battery. The trade you get with these cells is lower capacity.

 

[L]

I have been charging for 18 hours now and the phone is as dead as can
be .. original battery was 3.6V 600mAh new one is 3.6V 300mAh ...

Looks like that battery was DOA

Matt

 

[Mark W. Lund, PhD]

it is more likely that the charging circuit is haywire.

I have been charging for 18 hours now and the phone is as dead as can
be .. original battery was 3.6V 600mAh new one is 3.6V 300mAh ...

Looks like that battery was DOA

Matt

--
----------------------------------------------------------------------
Mark W. Lund, PhD ** Battery Chargers
CEO ** Bulk Cells and Custom Battery Packs
PowerStream Technology ** Custom Power Supplies
140 S. Mountainway Drive ** DC/DC Converters
Orem Utah 84058 ** Custom UPS
http://www.PowerStream.com ** Engineering, manufacturing, consulting

 

[L]

it worked (sort of) withthe NiCd'a do you think the NiMh battery killed
it?

Matt

 

[CWatters]

it worked (sort of) withthe NiCd'a do you think the NiMh battery killed
it?

No not unless the battery was faulty.

 

[Mark W. Lund, PhD]

I can't imagine that it could have, there is already a current limit,
so even if the cell was shorted it probably wouldn't have damaged the
charger.

The way to tell, of course, is to measure the current while the battery
is plugged in, but measuring the voltage when the battery is not
connected should also tell you if it is working.

If you don't have a voltmeter, get one. They are dirt cheap if you
get one at Harbor Frieght, etc., and are an essential part of any
man's toolbox.

Best regards
mark

it worked (sort of) withthe NiCd'a do you think the NiMh battery killed
it?

Matt

--
----------------------------------------------------------------------
Mark W. Lund, PhD ** Battery Chargers
CEO ** Bulk Cells and Custom Battery Packs
PowerStream Technology ** Custom Power Supplies
140 S. Mountainway Drive ** DC/DC Converters
Orem Utah 84058 ** Custom UPS
http://www.PowerStream.com ** Engineering, manufacturing, consulting

 

[JM]

quoting:

I have been charging for 18 hours now and the phone is as dead as can
be .. original battery was 3.6V 600mAh new one is 3.6V 300mAh ...

Looks like that battery was DOA

300mah, I think that's a typo. A NiMh pack made of the same physical size
cells and having enhanced ability to be continuously slow charged without
overcharging, this battery should be on the order of about 1300mah. If it's
not working, do as another poster said; check the charger. There is also the
possibility you received a defective battery with one shorted cell, bad
joint, etc. Yes, it happens.

 

[[email protected]]

it worked (sort of) withthe NiCd'a do you think the NiMh battery killed
it?

Alright, I'm definitely sticking with the NiCd. ;-)

 

[Dan_Musicant]

On Sun, 17 Apr 2005 00:11:54 -0400, [email protected] wrote:

:I recently bought a cordless phone, which came with a NiCd battery. In the
:manual it says:
:
:"To reduce the risk of fire, use only 3.6V 850mAh Nickel
:Cadmium (Ni-Cad) cordless telephone replacement
:battery pack."
:
:I've heard about the dreaded "memory effect" with NiCd batteries, so I'm
:interested in replacing it with a NiMH one. Someone who is selling a 3.6V
:1000mAH NiMH battery on Ebay claims it works with my phone, but will it really
:be safe? Wouldn't want to install a NiMH battery and have the house burn
:down.
My oldest cordless phone is still going strong, and I feel strongly that
it has NiCads, although I'm not certain. It must be around 7-8 years old
or more. I always leave the thing charging.

My other cell phones have been a different story. I have a Panasonic,
that replaced (by RMA) a previous version of the same phone, and they
have NiMH's. Both of these phone's manuals suggest not leaving the packs
charging for maximum battery life, which is certainly a PITA. It's much
easier to just leave it charging, since the base has to be plugged in
regardless for the phone to work. However, in deference to that
admonition I've not kept it charging but the first battery pack died in
less than a year in any case. The newer one is still alive after maybe
1.5 years, but I wonder about playing this game with it. NiMH's lose
their charge faster than NiCads, so I find I have to put it back on the
charger after 3-4 days or so and then guess when it's fully charged - I
have to look at the LCD and see if the indicator suggests a full charge,
not a game I enjoy.

I'd seriously suggest just using the NiCads in this phone of yours and
if and when they die, then think about replacing them, not sooner.