Invisible tanks could be on battlefield within five years

The only way this could work if they have a massive cooling system combined with it...

Unless you mean that the tank would have liquid nitrogen inside or something of the sort it's impossible to have a cooling system without having anything hotter on the outside of it (just look at the back of fridges, power sources of computers, the outside part of air conditioning.

To evacuate heat from one place you have to place it somewhere else.