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Manual Number 9019286 • Revision E, January 06, 2022
4.5 PERFORMANCE
Capacity
Capacity is the measurement of the energy stored in the battery and most often is used to
determine the length of time a particular electrical load can be operated. A standard measure
of rechargeable battery capacity is the current-over-time performance (measured in amp-
hours) called the “C” rate.
The C-rate is a function of the size of the load in relation to the capability of the battery. A 1C
rate corresponds to a constant current load (in amps) which the battery can supply for one
hour. The TB20 has a 1C rating of 20Ah and thus can supply 20 amps for one hour. Note that
many typical lead-acid batteries, and some lithium systems as well, are defined at a 1/20
th
(0.05) or 1/5
th
(0.2) C-rate. This is defined as the constant load that can be applied over 20 or
5 hours, respectively. For example, a lead-acid battery rated at 20Ah at a 0.2 C-rate can
deliver 4A for 5 hours (4A x 5 hours = 20Ah). However, that same system typically does not
perform linearly at higher C-rates. For instance, the same 20Ah lead-acid battery rated at
0.2C may typically only support a 20A load for 45 minutes, not a full hour, resulting in a true
1C capacity of only 15Ah. The capacity for these types of batteries is generally defined by a
logarithmic function of load versus time. So, when doubling the load, a lead-acid battery will
last less than half the time.
One of the significant advantages of lithium-ion technology is its constant capacity versus
load. As the load on the TB20 increases, its capacity maintains its rating proportionately. As
an example, if the standard 1C load of 20A is doubled to the 2C load of 40A, the discharge
duration is proportionally cut in half to 30 minutes. Doubling the load again to 80A would
deplete the battery in 15 minutes.
Summary of Contents for True Blue Power TB20 Series
Page 1: ...Revision E January 6 2022...
