The current drain would be any time the battery output was on, and you would also need a control and sensing circuit that would draw current.
You wouldn't likely need much cooling because it isn't normal for the battery to be passing large amounts of current for very long.
Components like this are used in full BMS systems which do have over-voltage, under-voltage, and balance management already, just not in any power sports batteries I am aware of.
The disadvantages are cost, some reduction of full output, complexity increasing odds of battery failure, fires, and that 2ma drain.
If the circuit were very high quality then any increase of failures would be extremely small as well as chances of fire being hugely reduced. But we're talking more money.
But 2 ma constant drain is a problem. By itself it would cause an earthX ETX18 to go stone cold dead in 4 months. Ad in some current for the sensing. circuit and the typical 1-3 ma most bikes draw all the time and your down to needing to charge the bike every 3-4 weeks of which avoiding is one of the primary sellers of LiFePO4 batteries over lead/acid.
Also factor in that although the internal BMS could be well designed, what the industry usually opts for kills more batteries then it saves. On a smaller scale these circuits are already on nearly every li-ma and li-co battery pack on the market and when you find a failed one, more often then not if you tear out the protection circuit the cells are still just fine.
It's a great idea and as technology gets better and cheaper it may hit the market and be an improvement, but so far has not.
Owned to date. Honda Aero 50, Honda Elite 80, Honda Elite 250x2, Suzuki Katana, Suzuki RF600, Yamaha YZF1000R, Kymco Xciting 500, Suzuki GS500, Suzuki Burgman 650, BMW F800GSx2, BMW S1000RR, Aprilia Scarabeo 200, Aprilia Caponord, Aprilia Sportcity 250
I love and miss you Jeneca and I'm sorry.