Battery

I have a Antique Auto battery that I bought in 2001 and now it's going bad, only puts out 200 cranking amps. Tried to save it by flushing and adding new acid. It didnt work.
Question is, has anybody cut the bottom off and fit a smaller battery in the old case? And used cables from the old terminals to the new ones. Seems like it might work.
Thanks for any help. Bob