February 18, 2009

REPAIR: Cordless Phone Battery Modification

My wife picked up a pair of cordless phones on Freecycle to replace our old phone that was dying a slow and staticy death. Unfortunately, one of the handsets didn't work when we plugged it in.

I suspected it was just a battery issue, and after swapping batteries between the two handsets was able to confirm my suspicion.

Since I had recently replaced the battery in the old phone, I figured no problem, just swap batteries. Or not, as it turns out the connectors between the two brands of phones are different.

There's nothing special about cordless phone batteries, in the end they are just 3 Ni-Cad AA's linked in series to give 3.6V at whatever capacity you want. The more milliamperes (mAh), the longer the talk time. In fact, you could easily buy your own batteries and wire them up to create your own battery pack. But, in this case I just wanted to swap connectors for a quick and dirty fix.

The swap is easy. Snip the wires on both batteries to remove the connectors. Strip a quarter inch or so of insulation from both the desired connector and new battery. The wires for both parts should be color coded red for positive and black for negative. Cross the stripped end of the red wires from the connector and battery and twist to create a connection.

If you feel motivated, the wires can be soldered together to guarantee the connection will not pull apart. I did not do this for two reasons. One, I was in a hurry to make sure the phone worked, and two, the soldered joint will be less flexible for installation in the phone. Another consideration is that the wires are not loaded once installed in the phone, so there is little to no risk of the splices being separated.

Now repeat for the black wires. When finished, wrap the wires individually in electrical tape to hold the splices together and prevent shorting. Re-install into the phone and you are done!

My phone has been operating on the modified battery for about a year now with no ill effects. In fact, we can't tell the difference between the two handsets unless the back cover is removed.

This method could easily be used to maximize the talk time for your cordless handset by utilizing a higher mAh battery pack than normal. You could also save a few bucks by picking the cheapest replacement battery available, regardless of brand and then adapting it to your phone.

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