[alanw]

Be careful with these. If it is an electronic circuit then even if it is waterproof it may have condensation issues like my oex bait timer did, which caused it to fail after only a few outtings.

Personally I avoid adding anything extra between my batteries and electronics because it's just adding another potential failure point.

To answer your question, on the item you linked I would expect it to draw 3A constantly from your battery. But, if I were to buy one of these I'd surely check it's actual current draw during use, and be prepared to return it.