freezing can cause damage to the batteries in some cases, because the maximum voltage they can handle is reduced at cold temps. don't charge them under 10 degrees to be safe, and don't feeze them below 5 degrees when they are at maximum voltage, like 3.8 or 4.2 per cell, because at freezing they can only handle 3,7 voltage, so maxiumum overcharges them. so if you freeze your batteries, make sure you use them for 5 minutes first, to get to 95 percent recharge.
if your bms has higher figure for the recharge, say 4.2 instead of 4, its especially important not to freeze them at those levels.
it reduces their maximum capacity and subsequently they can't recharge as high as they did.