I love listening to music while I work on projects and I was without a music player since the audio jack on my iPod broke. Using some money left over from an amazon giftcard, I decided to try out the Sansa Clip Zip. The device was super-cheap, could have its memory expanded with a micro sdhc card, and got great reviews on head-fi, so I was sold.
After the Zip arrived in the mail, I installed Rockbox. For those who don't know, Rockbox is an open source firmware that can be loaded onto a variety of media players. The best way to describe it is like linux for media players--its user interface leaves a bit to be desired, but it has support for practically every audio format under the sun and is delightfully hack-able.
Once I got used to Rockbox, I was happy with the device except for one gripe: the battery life. My old iPod got 20+ hours of playback per charge and the clip zip only got about 15 hours. I remembered reading a guide for replacing the battery on the clip zip, so I wondered if I could replace the battery with a larger capacity battery.
Research showed that the clip zip's battery had a somewhat common voltage for rechargeable batteries (3.7 volts) and that increasing the battery capacity would have little effect on the performance of the device. I found a cheap 3.7 volt LiPoly battery on amazon and ordered it. (in retrospect, this would probably have been a better battery to buy)
The battery I bought was a replacement cell phone battery, so the first thing I did was to remove the casing surrounding the battery and remove the charging circuit.
A quick word of caution here: BE CAREFUL. In general, you shouldn't take apart batteries. They have nasty chemicals inside, and if you use conductive, metallic pliers like me, it's easy to short circuit things. In my case, it turned out that the entire metallic casing of the battery was one of the electrodes, so I quickly insulated it with kapton tape.
One thing to notice is that the Clip Zip has 3 wires connected to the battery, not two. This is for the charging circuit. In general, most electronic devices with rechargeable batteries contain a charging circuit which ensures that you don't over-charge the battery when you have it plugged in for an extended period of time. The trick is to connect the battery to the charging circuit, not directly to the device.
Once I got everything soldered together, I tried booting the device. Everything seemed to look okay, so I insulated all of the components and tried fitting it back into the original device housing. I forgot that larger capacity batteries mean physically larger batteries, so I had to expand the device housing with hot glue and aluminum tape. Sure, it makes the industrial designer inside all of us cringe and has an uncanny resemblance of an IED, but it has that hacker appeal!
After using the zip for a couple of weeks, I can happily say that the hack caused a substantial increase in battery life. The original battery was 300 mah and lasted for approximately 15 hours of playback. The new battery is 1100 mah and lasts for 50-60 hours of playback. Given that I only listen to it for a couple of hours each day, that means I can go at least 2 weeks between charging. That, coupled with the total project cost of approximately $50 for the device, battery, and 16gb micro sdhc makes me a very happy hacker (I'm able to get 2.5x the storage space of the ipod touch at 1/4 of the cost)!
(I apologize for the lack of posts. I've been making the transition to college. Hopefully more posts will come soon!)