electrical:12v:battery_capacity

**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).^{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)} 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^{5)}

technically C/20/2, but that form is rarely seen outside formal documents

decimal vs. fractional expression, can be used interchangably

Lithium doesn't not have a significant Peukert effect. Capacity measured by C/20 and by amp-counting will be nearly identical

Due to lower internal resistance AGM is less affected by discharge rate and lithium is barely affected at all.

vhttps:*www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/11731-peukert-law-batteries-and-you#post11731))
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electrical/12v/battery_capacity.txt · Last modified: 2022/09/22 12:19 by frater_secessus