Keeping a cell phone out of the land fill

My sister recently came to me because her cell phone didn't seem to want to charge its' battery anymore. Verizon wasn't able to fix it. I ruled out the battery being the problem by plugging in a similar (known good) battery.

Apparently something is wrong with the charging circuitry. In the meantime while I'm figuring something out, we bought her a new OEM battery from eBay for less than $5 shipped. She used a spare cell phone in the meantime (which she doesn't like) to keep her going, but it is not a good long-term solution. So, I put on my little thinking cap as this was a challenge I was looking forward to taking on.

After much searching the 'net, I found a particularly useful web page:
http://circuitsdiy.com/usb-li-ion-charger-revision
What I liked about this one is that it doesn't use a dedicated lithium ion charger IC, which mostly seem to be SMD as opposed to through-hole. I don't have the tools/experience/knowledge to solder those kinds of components (yet), so was happy to find this circuit.

I already have half of the components required for the circuit, and it was only a couple of dollars to order the ones I didn't have, so I placed the order with DigiKey, and a few days later, I was ready.

First order of business was to breadboard the circuit based off of the schematic from the link above:

Then I needed an easy way to connect the battery non-permanently. I have a bunch of old cell phones in my 'junk bin', so I found one that might work, and disassembled it:

The part I needed is not shown above, but shown below after I soldered a couple of wires to the appropriate 'spring terminals' (not sure what they're really called):

Closeup of the soldered wires on the 'spring terminals':

Now we just need to connect the 2 wires to the breadboard:

And put the battery in:

Doh!! It doesn't work - FAIL! It only charges for a few minutes and not up to the voltage it should, so is no good. :(

I contacted the creator of the circuit and he gave me a couple of suggestions but it still didn't work. He ended up sending me a professional circuit board. When I got it, I soldered the components onto it:

So then I connected those 2 red/black wires from the top-left corner of the photo to the other 2 wires from my 'battery holder', connected the battery, and was another FAIL. :(

Not being the electrical engineer I would love to be, I didn't know what to do, or how to troubleshoot. I turned to one of my favorite online retailer of electronic components/widgets (Duh - Sparkfun!), and found the perfect thing. I wanted to avoid going this route (buying a pre-made product) as it costs more money and isn't as fun and educational as DIY. But, I had no choice.

Here's the board from Sparkfun with a Micro USB cable plugged into it (for supplying power) on the left, and a JST connector coming out on the right (to connect to the battery holder):

I know you probably can't tell, but this thing is small! It's so small I don't know if it's a good thing or a bad thing, but it works! When a battery is charging, there is a little red LED that lights up...when the battery is charged, it turns off. It's simple and small, and again, it works, so I'm very happy with it. Thank you Sparkfun. :)

To wrap this up, I performed a few more steps. I added a little bit of solder to the wire connections to make sure they stay together (circled):

Added some hot glue to keep the wires in place (they would never survive in my sister's bag otherwise):

Covered the bottom section with electrical tape in addition to the hot glue to help keep the poor wires from moving in her bag:

Then wrapped the exposed wire connections up with some electrical tape to avoid shorting the charger/battery:

All done! Instead of throwing her half-broken cell phone that won't charge the battery anymore into the garbage, she can now keep one charging/charged outside of her cell phone while the other battery allows her to actually use her cell phone!