Batteries on cordless phone not charging. Likely culprit: The batteries or the charging cradle?

Boy, the technology gods have it in for me this week! First my scanner dies (thanks to a defunct power supply, I concluded; see thread); now my cordless phone is circling the drain.

The unit is about 10 years old, but it has gotten very little wear and tear. The handset takes 2 rechargeable AA nickel metal hydride (NiMH) batteries. They are user-replaceable, not permanently soldered inside.

About a year ago the original batteries died, so I bought a 4-pack of off-brand NiMH replacements. I popped a pair of them into the handset, and they worked decently. They were not as robust as the original batteries, but they would last long enough for most phone conversations before requiring more cradle time.

Well, things started to go very sour about a week ago. The batteries would lose all their juice after just a few minutes of phone talk. I figured my replacement batteries had reached the end of their lives too, so I popped them out and popped in the 2 unused ones.

Same problem. There was minimal charging going on; despite the handset sitting in the charging cradle for hours, only 1 bar of the 3-bar charging meter would darken on the handset display. That leads me to suspect that maybe the charger inside the cradle is shot, not the batteries.

So, what do you think? Stale, old, cheapo batteries? Or a good charger gone bad? I welcome your thoughts.

BTW, I own a basic pocket-sized multimeter, if that will help diagnose the situation.

Thanks all, in advance.

I’m leaning towards the batteries being bad, given how quickly they failed, plus a failed charger would likely stop working completely since they are fairly simple, often just a AC/DC power supply with the circuitry inside the phone doing the actual charging, although older non-Li-ion phones might be different.

You could try using the multimeter to measure the output voltage on the charging contacts, which should be higher than the battery voltage on the phone (or number of batteries x 1.2 if it isn’t listed); a more sophisticated test would be to put a load resistor across the output while measuring; a significant drop in voltage with a light load would indicate a problem (load depends on its rated output; for example, for 100 mA at 3.6 volts, try a 100 ohm resistor (36 mA).

Of course, you could also try new batteries, but if it turns out that the charger or phone is bad, you might end up having to replace it (the batteries could be used for something else though).

I’ve worked in the cell phone business for…(quick math…) about 10 years. Similar issues with charging batteries. I’ve had a bunch of batteries go bad due to charge/discharge cycles. And some go bad due to testing. (Hey! Who wants to hook up a 12V charger to this system…backwards?)

I don’t believe I’ve ever had a charger go bad.

It can happen…but I think the odds are on the batteries.

Did the batteries come with a stand-alone charger when you bought them? Or do you know anyone else who has equivalent rechargeable AA batteries you could do some swapping with?

Thanks for all the advice so far.

No, I don’t have a stand-alone charger, or any other swap-out batteries.

Ok. You can still measure the batteries you have. I’d wait for them to almost die, and measure them. Then charge them…and measure them again. If the charge reads the same, you may have a charger problem.

My best guess is you’ll see a difference in the charge state, but you’ll be reading what we call a surface charge. It looks like a real charge as far as having the right voltage, but doesn’t really have any capacity - once you start to use it, it drops very quickly. It’s one of the common ways for a battery to fail.

If the charging contacts have any spring in them it’s possible the wires soldered to the charging contacts have come partly loose. This often happened on old school cordless phones.

If the phone is really 10 years old it might be better to simply replace it. Multi handset cordless phones with tons of features are dirt cheap these days and are often sold as loss leaders in store sales.