By definition, rechargeable batteries are capable of being recharged and few people give much thought to the duties of the battery charger. Some of the simplest are the constant voltage types such as those used as cheap car battery chargers, often consisting of little more than a step-down transformer and regulator, but these are far from ideal. Most modern rechargeable batteries are technically advanced and various different chemical processes are involved. Each type of battery has specific charging requirements and a good battery charger is one that provides efficient charging throughout the charging cycle, with regard to the optimum charging current and voltage at each stage and terminating charging when complete. More batteries are damaged by incorrect charging than any other cause, so it is vital that charging is carried out in as near perfect a manner as possible. Differing technologies are employed and some chargers use a combination of these. Constant current chargers are often used for NiMH batteries and NiCd batteries, with a voltage cut-off. Taper current from a crude constant voltage source is only suitable for some sealed lead-acid batteries. NiMH and Lithium batteries are unsuitable for trickle charging. Some intelligent chargers constantly monitor the battery status and may employ highly controlled pulse charging for maximum effectiveness.