While cold in it's self is great for electronics..... less noise etc it is not good for battery life.
Keeping the battery warm helps, but they get cold quick when in use.
There is a really great workaround for P Series backs. There is a Canon battery charger that also works as an external battery holder
that uses the same batteries as P series backs.
It comes with a connector with a dummy battery on one end and connects to the back.
You can use your regular back batteries or buy huge ones. The charger also comes with a belt clip.
You can keep the batteries warm under your coat and with two hefty batteries you can keep going for a loooong time.
Makes a great dual battery charger two.
They go for about $ 80 on ebay. It's a high quality charger too.