The short answer is that you can charge a 6-volt battery with a 12-volt charger. So, what's the catch? The catch is that it can be dangerous to do so. On the other hand, you cannot charge a 12-volt battery with a 6-volt charger. There is no danger in trying to charge a 12v battery with a 6v charger. There is not enough. Ideally, the best solar panel to use to charge a six-volt battery is a six-volt solar panel. Because solar energy ebbs and flows throughout the day, the panel will deliver less than six volts of current at its weakest power. In short, a solar charge controller or a solar regulator limits the amount of energy from an array to its components, especially for Solar. There are different types of solar regulators. They are PWM — Pulse With Modulation and MPPT or Maxim PowerPoint Tracking regulators, and they work differently. PWM Regulators— The keyword here is PULSE. You can charge a six-volt battery directly without a solar regulator, but you do so at significant risk. A solar regulator on the cheaper end is around $50. However, the regulator's cost is minimal.
