What C-rate means
The C-rate is current as a multiple of capacity. For a 20 Ah battery, 1C is 20 A, which would empty it in about an hour, 0.5C is 10 A and 2C is 40 A. Datasheets give the maximum charge and discharge rates this way, so the same figure works for any size of battery.
Typical limits
- LiFePO4: usually 0.5C to 1C charge and 1C continuous discharge, often limited further by the built-in BMS.
- Lithium-ion and LiPo: often 0.5 to 1C charge, and discharge from 1C to well over 10C for power cells.
- Lead-acid: charge at about 0.1 to 0.25C. At high discharge rates, the usable capacity drops noticeably (the Peukert effect).
For radio
A 100 W transceiver draws about 20 A on transmit. From a 20 Ah battery that's 1C, which is fine for a LiFePO4 but hard on a small lead-acid battery. The battery runtime calculator works out how long a battery will last for your mix of receive and transmit.
Questions
What does 1C mean?
A current equal to the capacity: 20 A for a 20 Ah battery, which would empty it in about an hour.
What C-rate can a LiFePO4 battery handle?
Typically 1C continuous discharge and 0.5 to 1C charge, but check the battery and its BMS.
Is 0.5C charging safe?
For most LiFePO4 and lithium-ion cells, yes. Lead-acid batteries should usually be charged more slowly.
Why does a lead-acid battery run out sooner at high current?
The Peukert effect: usable capacity falls as the discharge rate rises.