Actually, Battra is a separate entity from Mothra. Battra appeared in the 1992 Godzilla vs. Mothra, first as an armored caterpillar (with beam weapons from its eyes and horn), and later as a moth (kind of like a "Dark Mothra"). Battra's apparently mainly concerned with ecological threats to the Earth, and Mothra convinced Battra that Godzilla was a major threat, so the two moths took him on in a theme park. (I remember the enormous ferris wheel.)
Well, Haven't seen any godzilla movie other than the 98 american one. Not that bad, but not true to what godzilla really is, We want friggin' laserbeams from his eyes, and energy/fire breath dammit.
Most of my godzilla knowledge comes from the exellent Stomp Tokyo site.
The ultimate site for sci-fi, fantasy, horror, and B-movie madness, in the world!
And I am a big fan of B-movies. Two of the best sci-fi movies ever where B-Movies (The Terminator and Robocop. They just happened to become big successes).
Also my favourite movie in the whole world is a B-Movie (In the Aftermath, a very cool partly animated, partly live movie about the world after WW3).
The classic kaiju you mention, DRT, were all on my to-do list. Especially Anguirus. But I'm working on Gamera amd the Gyaos right now, so it may be a while.