GaoGaiGar is the 8th and last Brave Saga anime.
These series are very similar to each other and at the same time very different but they have a common trait which is "a kid and a robot interacting in a cute way", "extremely detailed combining of robots", "hot-bloodedness" and "epic mecha battles".
Which one did you see? I'm guessing GaoGaiGar?
Have you heard of Brave Police J-Decker?