The company announced that it is partnering with two other companies, ELIIY Power and Ube Industries, to develop a lithium-ion starter battery that would be used on mainstream models in place of conventional lead-acid units. Mazda plans to have them ready for use by 2021. The advantage here would be that 12-volt lithium-ion batteries would be much smaller and lighter than the lead-acid ones they replace. And lighter cars don't need as much fuel to move around. Plus, as an added benefit, making cars lighter also often makes them faster and better handling. This is why companies such as Lotus and Porsche have offered optional lithium-ion 12-volt batteries for some lightweight sports cars.
A potential downside to the use of these batteries is increased cost. Lead-acid batteries from your local parts store will run you between $100 to $150. AGM batteries could be between $200 and $300. As for lithium-ion batteries, Lotus introduced the option on the Evora 400 in 2016, and the option cost $1,690. Odds are that a company such as Mazda won't be absorbing all those costs, meaning that the cost of these future Mazdas could increase with a change from lead-acid to lithium ion.