When choosing between a 36V and a 48V battery for your e-bike or conversion kit, it's essential to know your motor's voltage requirements. If you're adding a new motor, check its specifications to see whether it supports 36V or 48V. If you're replacing an existing battery, examine your current charger. If it indicates 42V, it's for a 36V battery. If it shows 54.6V, it's for a 48V battery. Choose your replacement battery accordingly.