I just updated firmware to 22.214.171.124.00. At first I kept getting a check battery message, though the battery I was using was fully charged. I switched from a generic battery to a canon and all went smoothly. As for the new firmware I haven't tried it out yet with a EF-S 18-135.
I think battery monitoring must be a pretty common issue with Canons.
If I use Canon batteries in my C300, the on screen monitoring and "fuel gauge" works fine. I have some non-Canon batteries though, and with some of them it takes a loooooong time for the fuel gauge to show up, and with one or two of them it doesn't show up at all.
Guess it's just a Canon thing....
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