Sparkes may be able to shead some light on this one.
We've used modified sinewave inverters for charging batteries whilst on the road and riunning laptops and gear.
Advice from the manufacturers has been to contact the manufacturers of the equipment you are plugging in to check if it can be used with altered sine wave equipment!
We had imported battery powered tools that we could get no info on and the batteries and chargers appeared similar to others we used.
We've had two chargers cook the batteries and overheat, each time we've been lucky to smell the burning whilst driving.
I don't know how common this is and may be Sparkes can shed some light re this problem.
Any mains electrical gear that uses "Switched Mode Power Supplies" (SMPS), instead of "old fashioned" iron cored transformers to transform mains voltage down, (prior to being rectified to make it DC), is expecting to be fed with a pure 50Hz sinewave.
The SMPS works by "chopping up" the incoming wave at a high frequency, and only using a portion of each "cycle" to be transformed & rectified. Smaller transformers can be used, saving weight & volume. The resulting DC is monitored, and an error signal is fed back to alter the "chopping up", so that the correct DC o/p is maintained.
"Ordinary" generators do not produce a very sinusoidal o/p; this is fine to power heaters, mains lights etc, and, usually, anything with a "proper" transformer, but will cause anything with a SMPS to have problems. "Modified sine wave" generators have an output that is nearer a pure sinewave than "ordinary" ones, so some SMPS may cope, but it can't be guaranteed.
Also, if you are using a generator for, say, a mains drill, and also have the charger for a cordless tool plugged in, then the mains drill will produce lots of high voltage spikes on the supply, which can kill the charger ( I've done it, but only once!!).
Note "transformers" for 12V halogen lights, that are common in homes thesedays, are SMPS, not "proper" transformers, that is why they cannot be used with ordinary dimmers, as these chop up the mains in a similar way to a SMPS.