FlyPenFly and Henning - before the walls get stinky from a pissing contest, you might be talking past each other...
Batteries don't randomly alter their voltage and there are excellent regulation circuits in the cameras. The chances of a generic battery "glitching" its voltage is somewhere close to zero. Battery chemistry just doesn't work that way. If there is a quality concern with a generic lithium cell it is the number of cycles it will take and the risk of shorts/fires. It won't have a freaky output voltage, there is no way for it to over voltage the camera. It could run out of charge faster than expected though.
On the flip side, estimating remaining charge, giving fair warning and cleanly shutting down often involves a combination of "smarts" in both the battery and the camera. The result can be the some generics on some cameras (the GH2 being a good example) can result in the camera losing power without warning at the end of the useful charge of the battery. So far a few E-M5 users have reported something similar with some generics but it hasn't been clear if it was just a "fast" shutdown with little warning or if the camera actually cut-out in mid-operation. If the battery dies without warning then yes it is possible to end up with a corrupted filesystem on an SD card. Typically this means losing your last image. For video though you may lose the entire video in progress.
Ken
You are completely correct that this is possible, and sorry to all that I fired off the last message as I did. We all have skills and backgrounds that others are unaware of, and these should never be used to 'trump' a post.
Standard design in cameras today is though that a hard shut down is not allowed. In actuality, even with Li-Ion batteries the voltage (and power) doesn't drop to nothing from a 'full voltage' with zero gradient. Remaining power, even though no longer acceptable to the camera for LCD or shutter operation is used for a safe shut down. As I mentioned before, for there to be data corruption due to a battery, the cameras has to have a number of other issues; possibly production anomalies resulting in a defective camera. That a camera like the GH2 might get confused by poorly written firmware in a 3rd party battery is a possibility, although a faint one. Mine has never had a problem; on the other hand I've not tested EVERY 3rd party battery with it.
I've used probably 50 3rd party batteries in the last 10 years with no issues; not even on the various late model Pansonics and Canons that have proved difficult with 3rd party battery manufacturers. With the money I've saved I'm more than halfway to a Leica MM. I'll keep on this path.
I've ordered 4 batteries off ebay for the OM-D; I'll report how they work.
Henning