Electroless nickel-boron samples with 5 wt % boron were synthesized on mild steel with a bath based on sodium borohydride. Evolution of chemistry in the bath was followed during plating. Most reactive was consumed during the first half hour of the process. However, reducing agent and stabilizer concentration evolve differently: the use of sodium borohydride is limited by diffusion toward the surface, while adsorption on the surface of the sample is the rate-limiting step for lead tungstate. A direct link was established between the amount of stabilizer used and the surface of the sample; however, it cannot be applied to the use of sodium borohydride. A batch replenishment procedure for the electroless bath was developed by chemistry analysis at different stages of the plating process. This procedure allowed bath reuse and reduction of the number of new bath preparations.