A float can charge a battery but it will take some time. Float is generally designed to prevent battery from discharge. Done at a "slight" charge voltage ie 13.8 (12 V) and maybe a 0.25 amp. Current is kept low to keep both temp and evaporation ot minimum. A float of 1.5 A at 6.9 for a 6V sounds too high to me. Wont hurt anything as long as electrolyte kept at above cell top level.

Dan Bentler