Solar lights harness energy from the sun to provide illumination for outdoor spaces. These lights contain solar panels that convert sunlight into electricity, which charges a battery for later use.
Since solar lights use rechargeable batteries and most standard-use batteries are designed to be rechargeable, there isn't a difference between the two. Since most rechargeable batteries are Nickel Cadmium (NiCd) or Nickel Metal Hydride (NiMH,) they can be used interchangeably in solar lighting.
While there are a lot of different battery types out there to pick and choose from powering solar lights today, the most popular options are definitely nickel-metal hydride and nickel-cadmium options. Both of these batteries have significant advantages over the older, out-of-date lead acid-style batteries that they replaced.
Solar-powered lights need batteries in order to store the energy that they accumulate from the sun during the day. As soon as the sun goes down, the small solar array built into solar lighting stops producing energy so the bulb relies on the energy stored in the batteries to produce light.
Since the batteries used in solar lights are generally rechargeable batteries, you can use a battery charger that is designed to work with the same size battery (usually AA) to refill them. Using a charger is helpful if your lights have limited access to the sun or if they have been in storage.
Typically, solar lights will use 1.2 V (500 to 900 mA) NiCd or 1.2 V (1000 to 2000 mA) NiMH batteries. In both cases, sie AA is most common with up to 4 of these batteries being used. Less common, but also frequently used, are 3.2 V batteries.
Do solar lights & batteries need a protection circuit?
When you're talking about solar lights and batteries that are going to be left out in direct sunlight all day long, for days on end, you're going to experience higher temperatures and lithium-ion degradation. On top of that, these batteries can be pretty fragile and necessitate the use of their very own protection circuit.