On my Crystal game before the internal battery ran dry, I did it with a team like the OP, they were all level 45. Feraligatr, Togetic, Golem, Gyarados and Mew (traded from Blue, catght through the glitch).
However, my most memorable battle was the first time I fought him. I was training a Pidgeotto at the time, and it was only about level 29 or something like that (all the others were a pretty high level). because I was so young, I found him quite difficult, and all the other Pokémon has been knocked out. So I sent out Pidgeotto against Venusaur, his last pokémon, and kept using Fly. Because Venusaur kept using Solarbeam, I won.
Venusaur took in sunlight!
Pidgeotto flew up high!
Venusaur used Solarbeam!
Venusaur's attack missed!
Pidgeotto used Fly!
It's super effective!
And so on until it fainted.