Charging a lead sealed battery
As explained in my comments, 10 A (note capital for abbreviated units named after a person) x 0.5 h = 5 Ah capacity required per motor. Go for at least 7 Ah for some margin and decrease in capacity with age.



Figure 1. Sealed lead-acid batteries.

These have the advantages that they are robust, easily charged, can be mounted in any orientation, etc. You would have to purchase a charger to suit.

You may find suitable batteries in an old UPS, alarm panel, emergency lights, etc.