Thanks. I just bought one.
Would you, or anyone who bought this charger, happen to have any electronic test equipment on hand? Even a simple digital multi-meter would provide the ability to do a quick sanity check on the charger.
First off, it'd be nice to learn at what voltage the pack is brought to when the charger gives off its "I'm done" indication.
The Fujifilm OEM charger leaves my OEM and third party packs at 4.17 to 4.185V, which is typical for a decently designed charger. A charger should *never* raise the voltage in the pack above 4.2V.
Not all third party chargers bought off the internet actually do the job right. Some have been found to do silly, dangerous, things like apply a trickle charge to fully charged cells or push the cells way past 4.2V - both are *very* dangerous failures. Sadly the fact that a product is for sale on the internet isn't a clear indication that it has been tested and verified to adhere to known safe li-ion cell charging practice.
If you aren't absolutely certain of the conduct of your charger you can make using them safer by never leaving packs in them for extended periods of time and never leaving them run unattended (within earshot of your fire alarm). Chargers that employ the proper algorithm should deliver a fully charged pack in ~ 3 hours or less, depending on how much capacity was consumed while in powering the camera device.
With so many li-ion powered devices out there, and so many third parties looking to make a buck off the demand for replacement or spare cells/packs, there is ample opportunity for unscrupulous or simply stupid makers to flog bad and potentially dangerous products on to an unsuspecting public. After all, they are just batteries and chargers, just like the AA cells and chargers you keep your kids toys fed with, right?
Nope. Typical AA/AAA (and related) NiMH chemistry cells and their chargers are more or less intrinsically safe because the chemistry is safe, highly unlikely to catch on fire, go into thermal runaway, explode in a sealed device, etc.
On the other hand, li-ion cells are not intrinsically safe. They can be made safe to use with correct engineering - design of the entire system, from pack design, device design, and charger design.
You get an implicit guarantee that the OEM which includes a charger in their solution (like the X100, and its pack and charger) has looked at these issues themselves and taken an active role in the overall system design, or has subcontracted some of that role out... but the bottom line is the OEM is on the hook.
With third party packs, but even more importantly in my opinion, third party chargers, you have less assurance that the bits will work not only superficially but safely.