NiMh, NiCd, Alkaline…. lithium. Stuff you need to know about batteries, chargers…. testing and using batteries.

Volts – mAh – NiCD – NiMH

What’s it all mean and why should you care?!

It’s important to select the right battery for your application but sometimes that can be confusing, especially for the average person who does not deal with this all the time. Good news is, it’s not that difficult when talking about NiCD and NiMH batteries.

Volts: Each NiMH and NiCD cell has a nominal (average) charged voltage of 1.2v
The 2.4v battery packs we are discussing here are all 2-cells, no matter what the chemistry is.

mAh: Milli-amp-hours, AKA current… or better understood as ‘power’
Generally speaking, the more power the better! Your device will last longer doing the same stuff with a battery that can hold more amp-hours.
500mAh means the batter when fully charges should be able to provide 500 mA of power for 1 hour…. or 1000mA (1 amp) for 30 minutes. (I’m sure you get the idea)

As a battery ages it’s total capacity in mAh will diminish.

NiCD vs NiMH
Generally, these batteries are interchangeable… you can use  NiMH battery in place of a NiCD and vice versa. NiCD is better at handling complete discharging and often used in solar lamps. NiMH is better at handling larger power storage (more mAh!). Most modern devices use NiMH or Lithium but we still see NiCD on rare occasions. These Uniden phones are one of those. I have no idea why. There is no advantage to the NiCD battery in this situation. It must have just been a cost issue at time of development.

This voltage choice for a cordless phone presents an issue most people are not aware of.  Many of the more advanced components used in these phones require 3.3v or even 5v just to operate. How does a 2.4v battery even work?? Well they use something called a voltage multiplier circuit to up the voltage. This requires more mAh to compensate…. draining the battery faster…. so a phone that uses a 3-cell 1200mAh battery pack will last longer than a phone that uses a 2.4v 1200mAh pack…. not because of the voltage but the fact that the 3-cell device will not need to multiply the voltage to operate 3.3v components.

The Uniden DECT1580 phone original battery was a 2.4v 700mAh pack.
The Panasonic KX-TGA400b phone originally had a 2.4v 1500mAh pack.

You can and should use the NiMH 1500mAh battery pack in the Uniden phone but you cannot use the 700mAh pack in the Panasonic phone. There are a lot of merchants advertising 700mAh batteries for the Panasonic phone, simply because the battery looks the same and has the same connector. Unfortunately this battery may appear to work, especially for the short term when new, but it will only cause problems in the Panasonic phone!! Buzzing over the talk path, poor quality audio transmit and no link to base errors are just a few of the most common problems weak batteries cause in the Panasonic phones.

Is your Panasonic cordless handset going dead? Resetting? Does the screen go blank for a few seconds then give you an error to move closer to the base?

Typically this happens only at the most inconvenient of times… (while you are using the phone of course!) Most phones with this problem will work just fine as long as you leave it alone on the table or in the charger where it’s as useless as a glass of sea water in the desert.

So what’s the deal? Unfortunately this is a very common problem in many models of Panasonic cordless phones. It is caused by a drop in available power to the phone. It’s more likely to happen when the phone needs the most power (when on a call) and when the phone is being moved (as you handle it during a call).

Open up your battery door. Does the battery just clip in without any wires or coiled springs? Are there just two metal flat contact plates for the battery connection??? Like this…..

Panasonic cordless phone battery connection

This type of battery connection works fine with a new battery… a properly designed battery… and new metal contacts free of dirt or oxidization (at the peak of their conductivity potential). After a few years of use, maybe with an older battery or an aftermarket copy… your phone is very likely to experience this power issue problem. The flat contacts are not a very powerful spring and under a microscope the flat metal plates are only touching in a few tiny locations. All the battery power running through one area causes oxidization and reduced conductivity…. and as you jiggle the phone (in normal use) the battery can bounce ever so slightly causing an additional drop in moving electrons.

Old batteries do not help the situation.

panasonic lcd battery display

Your phone is just guessing when it’s telling you the battery is fully charged. There is no easy way to test a battery and these phones do not have the circuitry for any more than a guess that relies on how long it’s been in use vs. how long it’s been on the charger.  Old batteries have less force to push out those electrons and there is just no way for your phone to alert you to the problem.

To make matters worse…. the poor battery connection doesn’t help the life of your battery. A poor connection can cause the phone to charge the battery when it does not need it. Over-charging is bad… not horribly bad… but over time it can really kill a battery. Also, never letting the battery fully drain to it’s potential isn’t so great for it either. Every time your phone resets because of a poor connection, it’s probably deciding that the battery is dead and needs a full charge, even if it just did that 15 minutes ago. You may even notice your phone getting warmer in the charger.

Could it get any more confusing?

It seems like a straight forward problem that should be easy to spot…. real world experience does not agree however. I’ve seen plenty of instances when one battery works fine in one phone but has power drops frequently in another. Swapping around batteries isn’t always a quick confirmation of the problem or validation of a good battery.  Improving the contacts with springs doesn’t fix old batteries which can and do offer up the same symptoms all on their own. Even new batteries can be junk… poorly made… weak cells… old stock… defective… or even more likely –> quickly damaged by a malfunctioning over-charging, under using, poor battery terminal phone.

What can you do about it??

A new battery might help but really you need better battery contacts. At p1repair we install springs in every model that uses this type of battery contact. We tried other solutions, like beefing up the contacts with added metal… copper fiber…. conductive glue… even lead. They all helped a little but they did not solve every issue or last reliably.
Known effected models:
KX-TGA650b, KX-TGA450b