A 300 CCA battery of most any brand will work. Keeping it changed and the electrolyte level full are the best practices for battery life. Get you a trickle charger and hook it up when your mower is not in use. A trickle charger is cheaper than buying batteries once a year.
www.batterytender.com
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Battery Tender® Junior 12V, 800mA Battery Charger - Available at Walmart
Perfect for all lead-acid, flooded or sealed maintenance free batteries (AGM and gel cell). Complete 4-step charging program (Initialization, Bulk Charge, Absorption Mode, Float Mode). Automatically switches to float / maintenance voltage after fully charging the battery. If the battery voltage...