I've been using a Powerseed for over a year now, albeit it not in the capacity for which its intended, and now its battery is dead. It's a lovely little pod-like thing, with no obvious way to replace the battery, so I checked their website. To my chagrin, it said to send the unit back with $10 to have a new one installed. That's about the price of getting a new battery in a watch, so it's not totally unreasonable, but my DYI pride would be hurt in the process.
So, I dove in and discovered that you can carefully pry the Powerseed open with a flat edge, working slowly around all of the edges, until the top clears the little mounting posts. Be careful that you keep the small, rubber button-platform when the halves separate. Then, using a small screwdriver, you can scoot the dead battery from its holder and replace it yourself. It takes a standard CR2032 battery that's readily available for hearing aids and the like. Snap it back together, and you're back in business. That's $3 and 7 minutes of your time, versus $10, a trip to the post office, and waiting several days.
Also, if you find that your Powerseed gets accidentally turned on in your pocket, you can remove the bottom button-platform while changing the battery. After you do this, you'll need a pen or something similar to control the unit, but it'll never come on accidentally again.