Cheap test load: Automobile headlights, or similar 12-volt lamps or heaters that are rated as high as you can get them.
Batteries are nominally rated at a 20-hour discharge rate, so if they are rated 105AH each, that's based on 20 hours at a 5-amp load. (Ratings for higher and lower rates are usually also available from the maker.) One automotive high beam lamp (~65 watt rated) is a conveniently close load for one battery at a 20-hour rate.
And I'd agree with Cam--cycling them down to the 50% point should be enough.