In the older batteries the cell-connectors were still found on the outside of the casing. The single cells are embedded in black bitumen and can be replaced individually. Batteries were, at that time, quite expensive and also quite prone to breaking down. The problem: Within the cell structure, the softer lead does not stay in its place, through the chemical reaction it sinks to the bottom. Once enough has been collected, it causes a short circuit and the cell is ruined.
The next generation of batteries looks a lot friendlier in its light coloured plastic casing. The cell-connectors are now found inside the casing and are no longer replaceable. We still talk about the wet-cell battery. To prevent the soft mass from sinking in the cell grids, in the latest generation of this type of battery, the individual plates are packed into pockets.
The Silver generation (from Bosch) is a fairly dry battery. This additional description indicates the alloy used in the grids. It is (almost) dry through the use of glass-fibre fabric, which can be seen between the plates. It soaks up the sulphurous acid, thus allowing the chemical reaction to take place over a shorter period.
The idea behind this construction was, the smallest possible loss of the active mass, thus giving the battery a longer life. An additional advantage is the endurance, which it needs to cope with the, nowadays common, quick change-over from charging to discharging with a relatively high current flow. Other manufacturers add a gel to achieve similar effects.
The charging voltage of the older batteries, compared with the new ones, has been decidedly altered. It has increased from the original 13,8 to 14,2 V and lately, can even be as high as approx. 14,7 V. Thus, each battery-type must fit to the voltage regulator. Should the allowed charging voltage be permanently exceeded when in operation, even a new (old) battery will soon pack up. 09/10
The max. charging voltage of sealed lead-acid batteries is 2,35 V/cell