Cell basics
Temperature cut-off
The cell surface temperature at which a manufacturer discharge or charge rating ceases to be valid, commonly 80 C or 83 C on high-power cylindrical cells.
What it changes in practice
A continuous discharge figure is a conditional statement, not an absolute one. A rating of 60 A that holds only while the pack keeps the cell below an 80 C surface temperature cannot be used in a sealed housing with no thermal path. Where a manufacturer states a condition, it belongs next to the number; stripping it out to make a comparison table look tidy is how packs get built on ratings they cannot reach.
Why it matters when you specify a cell
Read the cut-off as a design requirement, not a limit to stay under. If the enclosure cannot hold the cell below it at rated current, the usable current is lower than the printed figure — measure the cell surface at maximum continuous current in your worst ambient, then write the derated figure into the specification.
Related terms
Read further
More in Cell basics
Other terms in this group
The vocabulary you need before you can read a data sheet.
18650 cell
A cylindrical lithium-ion cell roughly 18 mm in diameter and 65 mm long, the most widely tooled format in the industry.
Read the entry →21700 cell
A cylindrical lithium-ion cell roughly 21 mm in diameter and 70 mm long, offering about 50% more volume than an 18650.
Read the entry →Form factor
The mechanical envelope of a cell — cylindrical, prismatic or pouch — which sets the packaging efficiency and the interconnect method.
Read the entry →C-rate
Charge or discharge current expressed as a multiple of the cell rated capacity, so that cells of different sizes can be compared on the same scale.
Read the entry →Capacity
The charge a cell can deliver between its charge voltage limit and its discharge cut-off, stated in ampere-hours or milliampere-hours.
Read the entry →Energy density
Energy stored per unit volume (Wh/L) or per unit mass (Wh/kg), the figures that decide how big and how heavy a pack has to be.
Read the entry →