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Battery capacity in Amp-hours is written as C. 100Ah, for example.
C notation can also be used to describe the relative amount of current charging/discharging battery bank. For example a 50A load on a 100Ah bank would be C/2 (100/2 == 50).1). It may also be written as 0.5C.2)
Note: most deep cycle manufacturer's rate capacity at C/20, due to Peukert effect on lead chemistries (see below).3). In other words, a 100Ah battery will deliver 100A with a 5A load over 20 hours.
If you have a 200AH battery bank then C = 200AH.
If the manufacturer recommends max charging at C/5 the rate should be at or below 40A (200/5).
If the manufacturer recommends minimum charging at C/10 the rate should be at or above 20A (200/10).
If the manufacturer recommends max discharge (load) be 3C the rate should be at or below 600A (3×200).
If the manufacturer says that Absorption stage is complete when charging current has dropped to C/100 or C/200 then the current to watch for would be 2A (200/100) or 1A (200/200).
Because of the Peukert effect, lead bank measured capacities are strongly affected by dicharge rate. Sample data below is for flooded lead acid.4)