Methods and device for battery charging and diagnosis provide a measuring batter energy state in which charging strategy alternate with the minimize balance between battery energy state and charging energy in which the balance is existed in battery energy barrier. Variance battery energy barrier derives adaptive charging cycle and charging protection in to approach the requirements of safety, full charge and high performance for lead-acid battery. The charging cycle derives protection mode to adapt the initial battery energy barrier state, and derives diagnosis mode to adapt electrolyte activities diffusion state, and derives the charging mode in optimum strategy to adapt polarization, storage and saturation cycle by using measure battery energy barrier, and derives the alert indication mode to result the charging cycles and diagnosis, in which the output charging energy is derived as continuous and minimum energy in inhibit of reduce efficiency due to the violent agitation and the fluctuation phenomenon in appearance in charging cycle. This invention comprise Primary power supply unit, measurement and control unit, secondary side control unit and alert / indication unit to feature the functions with stable, safety, full charging, high efficiency, diagnostic and longevity charger.