There are a lot of different goals that military science might want to accomplish with powered armor. The obvious one is the armor itself; un-powered armor is a trade-off between degree of protection and weight, and powering it turns the trade-off into more a matter of protection, cost, battery life, and user issues. To clarify that last, a combat soldier just needs protection, but an urban patrol soldier also needs some ability to interact with non-hostile citizens while still being protected from hostile forces.
Once a suit is powered, it has the ability to solve another military problem, which is how much gear a soldier can carry. The exact mix of stuff an infantry soldier carries depends on the mission, but in general their load is (by weight) mostly ammunition and batteries. A soldier with power armor to help carry a lot more ammunition would be able to fire heavier weapons or fire more shots of the same sized ammunition.
Power armor would still be limited in range by batteries. Sure, it can carry more batteries, but it uses more batteries. I would expect that designs would include mission-specific trade-off choices; a soldier assigned to patrol a specific area all day then return to base for re-supply would need a different model of suit than one assigned to spend days out in the field. Current soldiers have to make the same decisions. (Do I carry a canteen or a water purification kit? Do I pack full meals or just some snacks to last me until I get back to base? Do I pack a sleeping bag? Etc.) But power armor builds more of those decisions into the suit; it's not as easy to change what goes into a pack as it is to change the size of the battery pack in a suit of power armor.
Anyway, as for Traveller, the lesson is that some power armor features will arrive well ahead of what it calls Battle Dress. As I see it, the difference between current-technology power armor and Battle Dress is that a current technology suit might be powered by a fuel cell or motorcycle engine, with an endurance of several hours, while Battle Dress runs on super-science batteries with enough endurance that the soldier doesn't need to make plans to deal with recharges. There's also the protective difference: present-day armor might withstand any kind of small arms fire, but not a support weapon like a 12.7 mm rifle, but Battle Dress can withstand just about any kind of slug-thrower short kinetic-penetration artillery.
