There are tradeoffs both ways. A user replaceable battery can extend the life, but it also introduces a way for water to get in and short it out, thereby drast

There are tradeoffs both ways. A user replaceable battery can extend the life, but it also introduces a way for water to get in and short it out, thereby drastically decreasing the lifespan. But given the overall power requirements for the device, ensuring that the battery is charged appropriately to extend the lifespan is pretty easy. My Philips is over 4 years old now and if I'm traveling for a week I may need to charge it once (never really tried to let it drain fully), and it gets used twice a day.