skropp

MDX-400: Read this from Wikipedia: "Li-ion chemistry is not safe as such, and a Li-ion cell requires several mandatory safety devices to be built in before it can be considered safe for use outside of a laboratory. These are: shut-down separator (for overtemperature), tear-away tab (for internal pressure), vent (pressure relief), thermal interrupt (overcurrent/overcharging)[4]. The devices take away useful space inside the cells, and add an additional layer of unreliability. Typically, their action is to permanently and irreversibly disable the cell." Or this from Cadex Electronics Inc: "Some lithium-ion batteries fail due to excessive low discharge. If discharged below 2.5 volts per cell, the internal safety circuit opens and the battery appears dead. A charge with the original charger is no longer possible. Some battery analyzers (Cadex) feature a boost function that reactivates the protection circuit of a failed battery and enables a recharge." That's what I've based my statement on. I can not say if it applies to all lithium-ion batteries, or even if the info is correct, but it's not something I've made up myself. The reason I asked about this is that I wanted to know if anyone has had any problems with non-sony batteries. But anyway, thanks for your feedback.

I agree on what you're saying about built-in protection of the lithium-ion batteries, so thermal run-away might not be an issue. However, these protection ciruits are usually designed to cause permanent shut-down of the battery, making it useless. About operating and charging at the same time, I don't think this will affect the battery much. Lithium-ion batteries are insensitive to cycling, but are sensitive to deap discharging and high temperatures. So it's better to charge/discharge them little but often.

What I was thinking about was if the charging circuitry in the device was optimized for the included battery, so using a battery which may have a lower internal resistance results in too high charging currents and the possibility of thermal run-away. But I guess that this isn't a problem since all lithium-ion batteries are basic the same.

Can you charge the battery in the player or do you have to buy a special charger for the 900 mAh battery?