If you are talking 6 volt golf cart batteries (my battery of choice), I use these. They go across the long edge on the top of the battery and you use threaded rod at a 45 degree angle to the opposite side base of the battery. This does require having something for the battery to set against on the opposite side bottom. Makes for a solid mount.
https://www.ebay.com/itm/Yamaha-Gas-Golf-Cart-Battery-Hold-Down-Plate-G1-to-G22-1978-UP-New-Parts/121680830113?epid=14024867329&hash=item1c54be1ea1:g:0UwAAOSwNSxVSTiz