Played a few times under zero, up to - 8C the battery will last. Under that I would be worried about the gearbox failing. If you want to play anyway, you can buy a stock pouch that strap to your gun stock to hold the battery and you can add hand warmers to keep it warm. GBBR guy's put these inside their mag pouch to keep them warm on cold days.
Hand warmers:
http://www.canadiantire.ca/AST/brows....jsp?locale=en
stock pouch:
http://www.airsoftgi.com/product_inf...oducts_id=6384