C notation
Battery capacity** in Amp-hours is written as **C. 100Ah, for example. It can also be expressed in Wh (watt-hours) or other units.
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).((Lithium doesn't not have a significant Peukert effect. Capacity measured by C/20 and by amp-counting will be nearly identical)). In other words, a 100Ah battery will deliver 100A with a 5A load over 20 hours.
Examples
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 (3x200). \\
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).
other than 20hr rates
Because of the Peukert effect, lead bank measured capacities are strongly affected by dicharge rate. Sample data below is for flooded lead acid.[3] C/20 capacity is multiplied by the factor below to find projected capacity at given discharge rates.
Example: our battery is rated at 100Ah when drained at 5A over 20 hours. If it is drained at 20A in 5 hours it will have an observed capacity of 70Ah (100Ah x .7).
1 Hour = .3 \\ 2 Hour = .5 \\ 3 hour = .6 \\ 4 hour = .65 \\ 5 hour = .7 \\ 6 hour = .75 \\ 8 hour = .8 \\ 10 hour = .85 \\ 12 hour = .9 \\ 16 hour = .95 \\ 20 hour = 1 \\ 24 hour = 1.05 \\ 36 hour = 1.1 \\ 72 hour = 1.25 \\ 100 hour = 1.30[4]