So what DO you do when the battery charger bursts into flames on orbit?
I'll reinforce your point here. Knowing something about the fire response strategy on ISS you do the following:
1) If you actually are lucky enough to witness the charger burst into flames, remove the power from it, hit the fire alarm, put on a mask, and expend a CO2 based fire extinguisher on it. The mask keeps you from asphyxiating yourself with the extinguisher.
2) If you don't physically see what happens (which is most likely, ISS is big and some modules may go unattended for hours) - the combustion products will trip off a cabin smoke detector in the module. That will stop ventilation inside the module and ring the alarm. In most cases, this will put out a fire in zero g - fires tend to smother themselves without gravity to force convection currents.
Meanwhile, not having any knowledge other than a smoke alarm from a module, the crew will converge in a safe haven in the vehicle away from the fire. Two (of the 6) may go forward to investigate with masks, fire extinguishers, and a hand held device to detect combustion products (mainly so they know if they are entering a lethal pocket of CO or other gases). Hopefully the module isn't a total fog of combustion products - if it is, the crew is likely to isolate it and leave it. If you don't know what the fire source is (because you can't see it), it may well end up that the entire module ends up getting powered down to ensure an electrical fire isn't being fed. This of course has some pretty serious ramifications as well - shutting down power to a module is not a simple event to reverse (since all the computers, cooling, lights, etc. go down with it). It's likely that collateral damage to a module's systems would happen if that were done.
Even if you do understand what happened and know it's out, the harmful gases from burning plastic aren't going to just go away on their own, they have to be scrubbed out with deployed fans and special canisters. It would take weeks to clean up.
Fighting a fire in a closed environment is very different than something you would do in your home. In zero gravity, most of the control is by prevention - don't use flammable materials, stop ventilation on a detected fire so it doesn't spread, don't use things that generate poison air when they burn, etc. Even a minor fire that many of us have encountered at one time or another (smoked electronics, plastic bag on fire, etc.) would be an extremely serious event in space. That's why so much time is spent making sure equipment conforms with fire prevention standards.
