greenmachine is prolly correct. Though I don't remember reading anywhere about Sony using trickle charging, it prolly doesn't hurt to poke around about it... Regarding the topic NH14WM with MZNH900, I recently purchased a new MZNH900 and got a NH14WM as a spare. I've just put it through one charge with the provided NH10WM to check that it was working and get an idea of the charging period so it looks good for trying the NH14WM. A point of note is that the MZNH900 appeared to have a bit of trouble charging it. I put it in the cradle to charge and it stopped rather quickly. A quick check showed 2 bars on the meter. I have (possibly stupidly) pressed the stop button for about 3-4 more times as it seems to have stopped after 20 minutes or so after each press. I don't know if this is that "initial charge problem" mentioned in the notes section of the packaging or if the charger just can't tell when it's full due to the extra capacity and possibly substantially different charging characteristics. Information on the NH14WM seem so revolve around it being one of the largest capacity gum batteries rather than anything more technical despite it being around for a while :/ I am currently using up the "first" charge of my NH14WM. I'll prolly be back to report if something really abnormal happens... but as of this moment, there is no bulging, even after whacking the charge button a few times.