I went with Duracell 6V Golf Cart batteries. They were reasonably priced and made in the USA. You can get a 10% discount if you order online from Batteries & Bulbs Plus and pick up in store.
https://www.batteriesplus.com/productdetails/sligc115
I installed them back in March and they have worked out great.
They also have a nice selection of the Duracell Group 27 12 volt batteries...
https://www.batteriesplus.com/batter.../bci-group-27m