12V solar batteries come in many different configurations because they serve many different uses. You can get a charger in different wattages, typically 15 watt or 18 watt. The higher the wattage the faster it can recharge the device. One of the principal advantages of using a 12V solar battery charger is that you can eliminate most of the specialty chargers designed for individual appliances such as cell phones, cars, laptops, and iPods. Something else you might consider would be a charge controller that prevails the rechargeable device from overcharging while being recharged. The charge controller typically has a light indicator indicating when it has finished charging.
There are many specialized types of chargers. 12V marine chargers are in widespread use. They can last for years. Solar cell phone chargers enable you to keep your cell phone charged without being near an electrical outlet. Another type of specialized charger sits on your car's dashboard. It plugs in through the cigarette lighter and keeps the car battery from discharging over time. Other 12V solar battery chargers fit in digital cameras and camcorders, even laptops, if the batteries inside them are rechargeable. To figure out how long it will take to recharge, find the average hours of the battery in the device you want to recharge and divide it by the amperage hours, rounding up by 10%. Another rule of thumb is that your 12V solar battery charger should recharge the device in less than 20 hours of direct sunlight. That is direct sunlight, not just it being sunshiny outside.
It is also important to know what the application will be for any solar powered batteries that you buy. Some batteries designs are set up for quick discharge followed by a long recharge (like car batteries). Other battery designs favor long hours of continuous use (batteries that power trolling motors, for example). The use to which the solar battery is applied will drive the decision about which solar battery recharger you decide to use.
Because solar batteries produce direct current rather than alternating current, their design is for 12V or 24V DC current. A common use is using solar power for a home. Inverters convert the 12V or 24V solar power to 115V AC power for the home. The solar batteries receive their charge from the solar panels and supply constant power to the home when it is too cloudy for the solar panels to produce power.