Telephone battery pack, NiMH instead of NiCD?

[seaside]

I think the battery in my 4 old home telephone is going bad. It's not dead yest, but I am getting low battery warning all the time.

The battery pack consists of 3 AA sized NiCD batteries, supplies 3.8V to the phone. It seems to me it is possible to make working battery pack for the phone by using 3 brand new rechargable batteries.

I have no NiCd battery at all, but I got at least dozen new NiMH batteries. I don't like the idea of spending 10 bucks for NiCD batteries or 15 bucks for new battery pack when I can have new phone at less than $30 or when I already had plenty of AA sized rechargables at hand.

So, what do you guys think? Can I use NiMH batteirs instead of NiCD in this case, or is it something you can't recommend?

 

[Marduke]

The phone is most likely a constant trickle charge, which will most likely kill the NiMH cells in short order. About $5 will get you four new NiCD cells.

 

[Lynx_Arc]

if you leave it on the charger a lot nimh will be toasted in a short time they do not do well trickle charging. I recommend using nicad, I know a place that sells the nicad battery packs for phones for about $1-2 each 3AA cells if you cannot find any.

 

[seaside]

Thanks guys,
I will get some NiCD batteries soon.

It seems like old NiCD battery pack is almost gone for good. I found a replacement battery pack at walmart, and it had "newer improved NiMH battery" on pack. I am happy that I didn't buy it.

So, recent newer phones that use NiMH battery pack do not trickle charge like old ones?

 

[Mike Painter]

Thanks guys,
I will get some NiCD batteries soon.

It seems like old NiCD battery pack is almost gone for good. I found a replacement battery pack at walmart, and it had "newer improved NiMH battery" on pack. I am happy that I didn't buy it.

So, recent newer phones that use NiMH battery pack do not trickle charge like old ones?

I replaced NiCads with NiMH well over two years ago on an 8 - 10 year old Radio Shack phone I have. It has been rarely used over that period but I can still drag it around the house for a day or so and it holds a charge.
I'm pretty sure the NiMH pack was the suggested replacement

 

[Lynx_Arc]

Thanks guys,
I will get some NiCD batteries soon.

It seems like old NiCD battery pack is almost gone for good. I found a replacement battery pack at walmart, and it had "newer improved NiMH battery" on pack. I am happy that I didn't buy it.

So, recent newer phones that use NiMH battery pack do not trickle charge like old ones?

the charger for them probably shuts off or a very very low current trickle safe for nimh. you could use nimh if you take care and calculate how much charge it needs each time and take it off the charger when done but most people leave them plugged in forever

 

[SilverFox]

Hello Seaside,

The original set up most likely calculated the charge rate based on the capacity of the cells that were originally supplied.

Since NiCd cells are lower capacity than NiMh cells, you can replace old cells with NiMh without problems. It is true that NiMh cells don't like a constant trickle charge, but they can tolerate it for awhile, especially if it is quite low.

Since most NiMh replacement cells will most likely have about twice the capacity of the cells you are replacing, you should get longer talk time as well. Keep in mind that if you use higher capacity cells it is going to take longer to charge them back up.

With NiCd cells being phased out, the newer phones are being supplied with NiMh cells, and they have an intelligent charger, rather than a simple trickle charger. Also, most replacement battery packs will be NiMh.

Tom

 

[seaside]

I connected 3 NiMHs, put it into the phone and it is working like a charm.

I told my significant half that this is different battery pack, not to place the phone on the charger unless I told her do so. But since when she listens to me? LOL. I will see how long it can stay alive. Will buy another phone if it craps out on me.

 

[jzmtl]

My old phone's nicad pack died and I replaced it with a store bought nimh pack (didn't know how to solder back then), it lasted I think 4 years under constant use which I think is pretty good. It died a few months ago and I soldered a new nimh pack and it's been working fine since.

So in my experience it'll be fine.

 

[Fallingwater]

So, recent newer phones that use NiMH battery pack do not trickle charge like old ones?

In my experience, all cordless phones trickle-charge. There may be a few more expensive ones that don't, but since I've never seen much point in buying anything that isn't bargain-basement for talking around the house, if such a phone exists I've never seen it.

 

[SilverFox]

Hello Fallingwater,

I recently picked up a Panasonic phone and it has a definite charging cycle. While charging it displays that it is charging, and at the end of the charge the batteries warm up. When the charge is over the charging display goes away.

I have run some tests and the charging time varies with the depth of discharge. Running some discharge tests indicate that it does a reasonable job of charging.

Tom

 

[fivemega]

This is absolutely possible without any harm to batteries.
I have replaced many cordless phone, cordless vacuum, cordless shaver and... Ni-Cad batteries with NiMH and all work fine for years with longer operation time.
My both cordless phone came with 700mAh Ni-Cad and charging current of 70mA which won't harm 2000mAh NiMH batteries because it's C/30
Charging time is very long and handset is on base for charging all the time when not in use.
Highest available capacity of NiMH AA cells was 2100mAh at that time.
Since I used cunsumer button type cells, there was no room for heat shrink.