Temperature affects the performance of a battery; however, as soon as you start using it or charging it, it heats up a bit, so I wouldn't take too much notice of all that hogwash; however, you shouldn't let your battery freeze, so don't leave it in the shed when the temperature goes down to minus ten. I can see a bit of a problem for electric cars that are parked outside in the snow for a week. It would be OK for just one night because the battery has a large thermal mass, so will take a long time to cool down, but the recent winters we've had with prolonged temperatures below zero could be a problem.
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