Having extra batteries for your camera is one of those no-brainer things. But do you normally have an extra battery charger for each of your battery types? Have you ever been in a situation where having a spare charger saved the day?
In principle I don’t want to have a single point of failure for any shoot. So I have duplicates of most of my chargers, although not quite all. I probably ought to get a duplicate for the batteries for the Hasselblad, for example, although I do have a fall-back because I always take my 7D as backup, and that has different batteries (and spare chargers, in fact).
But I have to admit that I don’t think I’ve ever really needed it.
The main use for the duplication is to charge more batteries in parallel, because you can usually
discharge them faster than you charge them on intensive shoots. So for stuff like the V-mount batteries which power the RED and the LED lights, I definitely want to have as many batteries recharging at once as I can.