In its most simple design, a batch system is just a water tank within a glazed box.
Batch collectors and systems
Batch water heaters do not involve pumps or a separated storage tank, anti-freezing elements, heat exchangers, valves or sensors...
A batch system is very similar to a flat-plate collector, with a greater depth (of at least 6 inches/15 cm). The water is heated directly in the collector (they are open-loop systems).
Advantages and Disadvantages
Batch systems is a cheap option with almost no maintenance. They are a reliable technology in appropriate climate conditions (non-freezy climates); but they lack versatility.
Unless in very favorable weather conditions, family showers will have to be conveniently scheduled; heating the water to reasonable temperatures may take hours, and since tanks are typically un-insulated, they will not keep the water hot for a long time.
Batch systems are inadequate for both cold and very hot climates, where snow and hot temperatures can cause damages; their weight can also be a problem: large batch systems are designed with multiple "panels" (the outlet of one panel is coupled directly to the inlet of the next one), which raises the issue of weight; large systems can easily weigh 200 pounds/90Kgs dry and 350-500 pounds (160-230 Kgs) filled, requiring a strong enough roof frame.
If you plan to install a large solar batch system, consider calling a roofing professional to assess and, if necessary, to reinforce your roof.
Uses and climate
As already mentioned, freezing temperatures can damage solar batch heaters; you will have to drain the water manually in freezing conditions.
But very high temperatures can also damage the collector; if the water gets too hot, the collector can burst or get damaged. You will have to use the tempering valve to prevent overheated water from entering into the system.
Prices and capacity of batch systems
Batch systems are simple and relatively cheap, though not as much as you may expect. They aren't mass produced products: hence their price. Smaller units (3’ x 8’ units, holding 30 gallons of water/115 liters) may cost you $1,000 - $2,000, plus the cost of installation, pipes and hardware.