Our VTech 900 mhz cordless / portable phone started having a hard time keeping a charge so off we went to Radio Shack for a new battery pack… “WHAT?!?!? $16.00… that’s about how much we paid for the phone! Thanks but no thanks!”
I pulled the battery pack out and looked at it a little bit closer. Basically all that is there is 3 AA NICD rechargeable batteries in series and put into a cute little package.
I can make one of these cordless phone battery packs myself! It may not be pretty, but it will work, and only be $3.00
So, here it is, my Do It Yourself (DIY) portable / cordless phone battery pack!
Here’s what I did:
1) First I got some of my NIMH batteries that are 1800 mAh (compare this to the 700 mAh NICD batteries that came with the phone. In theory I should get about twice as much talk time. $3.00, is about the price of this pack because Fry’s Electronics has similar NIMH batteries (2000 mAh) on sale at 10 for $10.
2) Next I used a hot glue gun to stick the batteries together (next time I’ll use some JB Weld 4 minute epoxy.
3) I cut out some small strips of copper and placed them in the same position that the contacts on the original battery pack and glued them into place.
4) I used some sandpaper to scuff the contacts on the battery terminals and soldered the wires to the contacts. This put all the batteries in series at 3.6 volts.
5) Finally I soldered the copper tabs to the positive and negative terminals of the battery pack. Here is the monster below:
Like I said, it isn’t pretty but it works great!
This sure was a fun modification / project, and was really easy. As with many of my projects the first build is a bit rough (I don’t want to spend too much time on aesthetics if the project isn’t going to work). With subsequent builds I’ll use:
- JB Weld Epoxy to stick the batteries together.
- A better solder job (maybe use the tabbed batteries you can get on eBay)
- Shrink wrap to make the whole thing really pretty.Another option is to pull the original pack apart and use it as my case for the batteries.
- NIMH vs. NICD:
Nickel Cadmium (NICD) take an “overcharge” better than Nickel Metal Hydride (NIMH). Portable phone chargers are “dumb chargers” because they don’t sense when a battery is fully charged and keep charging at the same rate. People say that this is okay for NICD, but bad for NIMH and will damage the batteries. Others argue that because of the higher capacity on the NIMH that overcharging isn’t an issue. To be on the safe side I’m going to try to remember not to let the phone stay in the charger for days in a row.
- VTech Phone:
Before doing this cordless phone battery modification I put 3 AA NIMH batteries in a battery clip to see if the NIMH batteries I had would work. I hooked the wires from my battery clip to the phone and it wouldn’t turn on… it would just beep three times! I couldn’t figure it out. The voltage was the same as the original battery pack.I put the original pack back in and hit the on button, but the same thing happened. At first I thought I broke something, but then I had an idea. I took the phone and put it in the charger and pulled it out. The phone worked fine! From this I discovered there is something about the phone that requires that I “reset” it in the base before it will work properly.