Battery chargers only work well with rechargeable batteries. Whether solar powered or not, there’s 4 types of battery chargers. Quick chargers can fully charge a dead battery in an hour or less. They require careful control and measurements, and can reduce battery life. If done improperly, quick-charging can even be dangerous. Normal charging goes slower, typically charging a dead battery in 8 to 10 hours. Charging must stop when the battery reaches full charge or the battery may be damaged. Trickle charging feeds the battery even more slowly, so that you can leave the charger running for a while without reducing battery life. Rechargeable batteries slowly lose their charge over time, even if they’re not being used. A battery maintainer provides just enough current to keep the attached battery fully charged.
Many products are designed specifically as a solar AA battery charger. Good units include a charge regulator, and can typically recharge dead AA batteries in about 4 hours. The best units include boost circuitry to go from the 2-3 volts you get from a couple of battery cells to the 5 volts needed to run and charge USB-powered personal electronics. Solar AA chargers are usually fold-able into a small, light package. They’re great as a solar phone charger. By camping with solar you can keep your electronics going for weeks, months, or longer.
Most solar battery chargers are essentially solar automotive battery chargers, designed for 12-volt lead-acid batteries (including sealed gel cells). Some are ready to use, others require some assembly and hook up. Products range from a watt or two to nearly 100 watts.
The most common are battery maintainers, which can plug into the cigarette lighter socket or clip directly to the battery, and usually fit on the dashboard. They great for vehicles used only rarely, or parked for a long time at the airport. They can keep your RV, ATV, or boat always ready to go. Larger units, around 1 foot square provide up to 25 watt-hours per day. They’re more like trickle chargers and can also power electric fences and other remote loads. Given a week to charge up a battery, they can even provide a day or so typical use of small personal watercraft, radios, lights, small TVs, and more.
Larger photovoltaic solar panels need a charge controller to provide good normal charging. The controller is important to prevent battery over charging and over discharging, providing longer battery life. Most are also great RV solar panels. Batteries should be sized for about twice the daily photovoltaic panel output. Average usage should then be about equal to the solar panel output. This reduces battery discharge to about 50% for longer battery life, and brings the charging current down into the normal range.
That only leaves quick charging. I’m not sure if that’s really appropriate, but you could use a large solar battery charger to power a quick-charge controller.
Photovoltaic solar panels are well matched for battery charging. They provide direct current and can be configured for just the right voltage. Prepare to pay $10-$20 per watt for a solar battery charger. But compared to the cost of running power wiring, $1-10 per foot, the cost can be very attractive. And each watt of solar power panel will averag