My recommendations:
Small scale for hatchlings and mice
Large scale for yearlings and up
Weighs in tenths of grams. Perfect for sorting mice. Weigh babies in their deli cups. Uses 2 AAA batteries. It comes in various weight limits- the smaller one won't weigh heavy enough if you're weighing weanlings. The larger limit models would be okay- but you'll have a hard time fitting a 400-500 gram snake on it without doing a balancing act.
This scale has a nice clear bowl that snake will stay put in. You can (should) buy the optional AC power adaptor for $5.50 and never worry about batteries again. But if you _do_ need batteries, it takes 3 AA batteries, not obscure watch batteries. Lifetime warranty. Make SURE you save the receipt and the registration card, though.