There are two categories of sealed
lead-acid cell. These are the non-recombining or partially
recombining type, such as those manufactured by Sonnenschein and by
Crompton-Parkinson Ltd, and the fully recombining types, as
manufactured by the General Electric Company and by the Gates Rubber
Company. The fully recombining types are also produced in the UK
under licence by Chloride Energy Ltd under the trade name Cyclon.
Particularly towards the end of charge
and when being overcharged, the sulphuric acid electrolyte in
lead-acid batteries undergoes electrolysis to produce hydrogen and
oxygen.
Consequently, in service, the
electrolyte level drops and the concentration of sulphuric acid
increases, both of which are deleterious to battery performance and,
unless attended to by periodic topping up with distilled water, will
lead to the eventual destruction of the battery.
Aware of this danger manufacturers
recommend a periodic topping up of the electrolyte to the prescribed
mark with distilled water. The need for regular topping up has in the
past limited the applications in which lead- acid batteries can be
used. Manufacturers have adopted two methods of avoiding the need to
top up lead-acid batteries:
1. The development of non-recombining
or partially recombining batteries in which, by attention to battery
design (new lead alloys for grids, etc.) and by using more
sophisticated battery charging methods, gassing is reduced to a
Aninimum and topping up is avoided.
2. The development of fully recombining
types of battenes in which any hydrogen and oxygen produced by
gassing is fully recombined to water, thereby avoiding loss of
electrolyte volume.
Both methods have been used to produce
a range of non-spill either partially or fully recombining sealed
lead-acid batteries which are now finding an everincreasing range of
applications for this type of battery.
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