A Cordless Phone's Major Problem - Dealing w/ Batteries?

Brian James asks: "I am sick to death of cordless phone batteries going dead at the drop of a hat. And with frequent recharging they tend not to hold much of a charge. Replacement often equals the cost of a new phone altogether... so what's the point? Ultimately I wish cordless phone manufacturers would design a phone that used standard rechargeable batteries, preferably with 2 battery bays and a switch that allowed you to switch over to the fresh set when one set starts to go dead (of course, I don't see this happening any time soon). Is there any way to modify a cordless phone such that I can run the handset off of standard batteries? I don't care how 'cheap and dirty' it ends up, I just need to know I can pop in a fresh battery and call the guy back, without waiting 8 hours for it to charge up." A few cordless phone manufacturers do have a clue. Some phones allow you to charge an extra battery in the base while the other is being used by the phone, which works well (I have a Sony 900Mhz model that does this). It would be interesting to see if someone has done what the poster has asked, however if you'd like to recommend a cordless phone that keeps downtime to a minimum, I'm sure such would be appreciated.

Comments

In my expirence

[seann]

at Radioshack, I've dealt with people like you over and over again. They bring back their nickle Cadium based phones a few weeks later, and tell me it's dead. I then say "heres your new battery" and they buy it.

Now when the old couple comes in with the pre-1980's cordless phone, and I tell them the batter is 40-60$, I generaly ask if they want a new phone.

So I bring them over to the wall and show them the selection of phones with a lithium-ion batter in them, and I tell them about how if they keep charging their old battery (nickle cadium) it will damage the battery, but instead with these lithium-ion phone batterys, give them one good charge on your first use, then recharge them any time you wish!

The same thing is with my cell phone, the Sanyo SCP-4000. Not a spectacular phone, but the default lithium-ion battery that comes with it is a god send, I recharge it every night with no fear of the battery dying.

So in short I tell you, pick a cordless phone that has a lithium-ion battery in it, instead of a nickle cadium, or nickle metal hydrate (the latter is your next best alternative).

dyi

[elfkicker]

You can always make your own to save yourself a few bucks. Of course, it's probably more trouble than it worth. But, if you're the DYI type check out http://www.rccentral.com/guides.asp?ATCL_ID=51

That'll give you a little primer on what's involved. It's geared towards hobby RC cars, but you could adapt this for phones pretty easily.

I also make it a point to stay with NMH batteries when possible. They actually get batter after a little use, and no need to drain them completely before you charge them again.

Solutions: 1) Don't charge so much. 2) Discharge.

[Futurepower(R)]

I'm surprised no one else has said this:

Nickel Cadmium cells have 2 unfortunate limitations: 1) They have a "memory effect". 2) Charging them all the time makes them old very quickly, and makes the memory effect much worse.

So, this is what you do: 1) Don't charge the batteries all the time. I have two ATT 900 MHz Cordless phones. (I bought one for $30 at Costco, and the other for $5 at a garage sale. These are not expensive phones.)

I charge the batteries for about 6 hours once a week. I regularly talk for 3 or 4 hours in one phone conversation, and I have never had problems with the battery going dead. I've never switched phones in the middle of a conversation, either.

If I have a conversation lasting more than 20 minutes, I charge the phone then, also, after the call.

This is how you tell if you should stop charging a NiCad battery: It becomes warm. That is because all of the charge energy goes into making heat after the battery is fully charged. Before the battery fully charged, some of the charge energy goes into charging the battery, of course.

Don't worry about overcharging a little. A few extra hours, even 10 extra hours, in one or two charges a month seems to make no difference. It is 24-hour, 7-days-a-week charging that causes the problems.

2) The memory effect can be completely cured by discharging the battery completely. To do this, buy a 510 ohm, 1/4 or 1/10 watt resistor (an electronic component) at Radio Shack or an electronics parts store or an electronics surplus store. Remove the battery. Just push the leads of the resistor into the contact sockets of the battery (where the contact pins normally go), and leave it for 12 hours. Once the battery is discharged, it will no longer have the "memory effect" and will be as good as new, or 95% as good as new. Then, recharge the battery until it is fully charged (when it becomes especially warm).

The memory effect works this way: It causes the battery to discharge rapidly, even though there is a small load. The memory effect causes the battery to have a "shallow discharge curve", they say.

Lithium Ion and Nickel Metal Hydride batteries do not have memory effect. However, they also get old faster if they are constantly charged.

This is reliable information. I was an electronics designer in past years, and I have talked to an RCA battery engineer about the exact parameters of NiCad memory effect.