An introduction to combi drills: The combi drill combines a hammer action and drill driver function enabling drilling into concrete and brick as well as wood, metal or plastics. Combi drills are cordless; see percussion drills for their mains equivalent.
To choose between combi drills: The key consideration when choosing a combi drill is the maximum drilling diameter required. 13mm refers to maximum drilling diameter in concrete & brick. You can use a larger drill bit for metal, plastic & wood (& some machines allow this in concrete & brick too) providing it has a 13mm or smaller diameter shank to fit the chuck. A keyless chuck is tightened by hand.
To make sure you’ve got the right combi drill – 13mm keyless chuck: Choosing the right battery: Cordless (or battery powered) tools have various chemical battery types; Li-ion is the latest technology, prior to that it was Ni-MH and Ni-Cad was the original. The higher the Ah (Ampere hours) the longer the interval between charges; the fewer times you recharge a battery the longer it will last. Some cordless tools can also come without batteries – also referred to as naked, bare units or body only. These tools are supplied without a battery or charger and more often than not without any accessoires. As a result they are significantly cheaper in price.