in a lead carbon battery, carbon is added to the negative plate which results in a much longer life. in fact, the added carbon gives the battery electrode many of the properties of a super-capacitor, which improves charge and discharge performance. partial state of charge (psoc) performance is also much improved, with almost no sulphation between 30 and 70% soc. sulphation is one of the primary causes of failure of traditional lead acid batteries and is generally caused by partial charging and ageing. sulphation is when sulphate crystals grow on the negative plate. in normal use, most of these crystals get re-absorbed when the battery is charged - however when the battery is left in a psoc, some of these crystals attach permanently to the negative plate. this in turn reduces the surface area on the negative plate, which in turn reduces the capacity of the batteries https://www.solar-wind.co.uk/off-grid-power-blog/post/lead-carbon-batteries.html