Image via WikipediaBattery care for SLA (sealed lead acid) photographic and video batteries | Creative and business resources for photographers - ProPhotoNut
Some battery chargers are quite good at recovering a battery from a fairly deep discharge by using a pulsing phase cycle that dislodges sulphur build up on the plates but no charger can perform miracles. If your battery has been left to go completely flat then it will need replacing but don’t panic because they are not expensive. In the UK we have MDS battery and Battery Masters among the online traders that stock the most common sizes. In most cases a battery can be replaced without the need for elaborate tools. The battery connectors are usually the Lucar spade type and the leads simply push on to secure. A Broncolor Mobil pack has just four small cross head screws securing the cover to the battery carriage. Undo these and a battery swap can take less than a minute.
An SLA battery does not need to be periodically discharged in order to maintain it’s performance, in fact, it is best kept in a fully charged state. An SLA battery can be kept on charge indefinitely if a high tech charger, like the Ctek, is used. Cheap chargers have no monitoring and can overcharge and destroy a battery if the battery is left on charge for too long. Basic chargers also have poor voltage regulation leading to a shorter battery life.