NiCd battery packs losing charge

[metroplex]

I have a pair of Uniden cordless phones that use 3xAA NiCd battery packs (600mAh) that are starting to lose their charge FAST.

If I leave my phone off the charger for about 3-5 hours, it tells me it has a low battery charge even though it had been on the charger for over 2-3 weeks.

What can I do to prolong the life of the battery and fix the current problem?

It sounds like the memory effect which has been labeled a false issue with NiCd batteries by so-called experts.

 

[kenw]

Nicad memory is somewhat misunderstood, but not "false".

the batteries are just worn out, whatever the reason may be. replace them. and plan to replace them as long as you have the phones. They aren't that expensive compared to new phones......

special treatment for the new ones? just the same stuff you've heard for years: discharge them pretty far before recharging. It won't do miracles but it will make them last longer than a lot of very short discharge cycles. But they too will wear out over time.

It would be difficult to replace them with anything other than nicad due to the different charging circuit normally needed for other chemistry types such as Lithium.

You may find that you can build a new pack yourself with off-the-shelf NiCad AA cells.

 

[JohnnyO]

I've been buying name-brand cordless phones, nevermind that the stores have a crapload of batteries, I can NEVER find what I need and end up buying a new phone every time I need a battery.

 

[keith]

Leaving a NiCd on permanent trickle charge seems to kill them in a year or so. It's better to only charge them when they run down, and the rest of the time, do not trickle charge. I used to work at Black and Decker and we tested all kinds of batteries in all kind of ways.

'Memory effect' as such is a symptom of incorrectly charging the NiCd. It's real but can be avoided. In a cordless phone you should be able to get 3 or 4 years out of the battery before it needs replacing.

 

[Al]

At todays prices the phones are pretty much of a "throw away" item.

 

[metroplex]

How about this:

I'm going to go home and find some resistors to help discharge the battery packs?

Or is there another way to discharge them fairly quickly w/o damaging the cells?

 

[eljefino]

If you can get the outer wrapping off the pack, and discharge each cell individually (there are 3) that might help. One cell has, through manufacturing tolerances, less capacity than the others. As the battery dies that cell actually gets current forced through it backwards. This isn't very good for it.

When my phone battery conks out I just get a whole new phone from best buy for $5-10 after rebate. Cheaper than the replacement pack.

Service replacement AAs from radio shack have nice solder tabs for rebuilding battery packs. Regular store bought AAs lack these making soldering harder. NiMH cells have 2000 mA-hours compared to around 700 in cheapie NiCds, probably including those in any new phone. So you could build yourself a very long lasting phone if you can find NiMH cells with solder tabs. NiMH charges fine on NiCd calibrated equipment.

Also look at "Big Lots" of all places for those phone battery packs at a reasonable price.

The resistor for discharching is a good idea. A flashlight bulb will work and tell you it's "done". The phone won't run the cells down to zero volts; it'll shut off. The only hazard is reverse charging a cell as mentioned earlier. But if you split the battery open and discharge each cell individually that'll work too... but it's more work.

 

[1sttruck]

We found a drop in high capacity NiMH (?) battery for an older phone at Radio Shack, which worked much better than the stock item.

 

[Schmoe]

Don't ever let them discharge backwards. Will kill them. Also, heat is the biggest battery killer. Keep them cool as possible. My 18V cordless seems to kill battery packs every year, regardless of use. I know one thing, if you absolutely don't have a need for anything cordless, save your money and go corded.

 

[HardbodyLoyalist]

When you buy your next phone, look for one with a NiMH (nickel metal hydride), or better yet, a Li-ion battery. They cost more, but last 5-10 times longer.

 

[cangreylegend]

LiOn is also bad news. Why? they have a shelf life of only three years or so. Regardless of babying and non-use. When you buy anything Li On, check to make sure you have the freshest cells. Those things are planned obsolescence. I always prefer NiMh standard batteries. I can't stand getting taken for propietary size battery packs.

 

[metroplex]

I understand the benefits of NiMH. High capacity, low cost, fast charging, etc... but they also lose their charge in storage faster than NiCd and Alkaline but the benefits totally offset the negative.

I use NiMH for everything... my Fuji S5100 uses 4xAA NiMH (2.5 Ah) and they're still on the same charge for the past 2-3 weeks after taking about 500 photos.

Right now I have some LEDs discharging the NiCd packs and they're working rather well. I started from 3.9V (3.6V pack) and its whittled down to 2.7V

 

[cangreylegend]

DO NOT COMPLETELY DISCHARGE THE NICD!!! This is a recipe for instant death. NiCDs should be discharged until about 0.7V per cell. Any lower than that it's a sure recipe to kill them. Ideally they should be charged with a constant current source. This is where the voltage is continually changed and current maintained. Unfortunatelt this a charger with a built microprocessor. There are chargers that hook up to PCs that can do this. You can try and "fix" them by exercisiong them, and will improve them if you charge them up then discharge them till .7v per cell is reached. For a 3 cell that's 2.1V. Do this at least three times, you'll see the difference.

 

[JohnnyO]

quote:

---

Originally posted by Al:
At todays prices the phones are pretty much of a "throw away" item.

---

If I need a new cell phone battery, it's usually cheaper to get a whole new phone from Nextel than just the battery.

 

[rpn453]

You need new batteries.
I wouldn't even think of buying a Ni-Cd battery anymore, but phones with Ni-Cd batteries are great because Wal-Mart sells Rayovac NiMH batteries to replace them (for $17 Cdn) and they're the same size, so I'm getting about 8 hours of talk time out of it. The ones that come with the NiMH to begin with tend to have smaller batteries that don't last nearly as long.
If you can't find a NiMH battery, you could easily make one with three AA NiMH cells.

 

[metroplex]

How do you charge your NiMH battery packs? on the phone charger? That will easily destroy your NiMH batteries...