Why are all the batteries different?

I have a 1D3, 5D2 and a G10, my wife using a 450D. All use different batteries and require different chargers which is a total pain when travelling. (I am ignoring my son who uses my old 1D2 because I accept that is a NiMH rather than Li-ion)

I can understand that the 1 series need a more powerful battery than anything other than my car to cope with the potential use, but that of the 450D, G10 and 5D2 are fairly similar in size (and also to the old BP511).

Even if Canon have to have such different specifications that no camera can share batteries with another, could they not at least design their range so that the terminals were in a similar position and a "universal" Canon charger could be used rather than having to take 4 on holiday with us?

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