Size battery banks for standby, UPS and renewable energy systems — with temperature correction, aging factors and depth-of-discharge limits per IEEE 485 and IEC 61427.
| Step | Description | Formula | Result |
|---|
| C-Rate | Discharge Time | Example (100 Ah battery) | Typical Application |
|---|---|---|---|
| 5C | 12 min | 500 A | Engine cranking, high-power pulse |
| 2C | 30 min | 200 A | Power tools, EV acceleration |
| 1C | 1 h | 100 A | UPS, emergency power |
| C/2 (0.5C) | 2 h | 50 A | Telecom backup, short-duration standby |
| C/5 (0.2C) | 5 h | 20 A | Solar storage, cycling applications |
| C/8 (0.125C) | 8 h | 12.5 A | Substation standby (IEEE 485 typical) |
| C/10 (0.1C) | 10 h | 10 A | Standard rating reference (IEC) |
| C/20 (0.05C) | 20 h | 5 A | Lead-acid rated capacity (C₂₀) |
Note: Lead-acid batteries are typically rated at C/20 (20-hour rate). When discharged faster than rated C-rate, effective capacity decreases due to Peukert effect. Lithium-ion batteries maintain capacity better at high discharge rates.
| Temperature (°C) | Lead-Acid kt | Li-Ion kt | NiCd kt | NiMH kt |
|---|---|---|---|---|
| -20 | 1.590 | 1.400 | 1.500 | 1.500 |
| -10 | 1.350 | 1.200 | 1.300 | 1.350 |
| 0 | 1.190 | 1.100 | 1.150 | 1.200 |
| 10 | 1.110 | 1.050 | 1.070 | 1.100 |
| 15 | 1.070 | 1.030 | 1.040 | 1.060 |
| 20 | 1.040 | 1.010 | 1.020 | 1.030 |
| 25 | 1.000 | 1.000 | 1.000 | 1.000 |
| 30 | 0.980 | 0.990 | 0.990 | 0.980 |
| 35 | 0.960 | 0.980 | 0.980 | 0.970 |
| 40 | 0.940 | 0.970 | 0.960 | 0.950 |
Reference: IEEE 485-2020 Table 1 (lead-acid), IEEE 1115-2000 (NiCd). Li-ion and NiMH factors are industry-accepted engineering approximations. kt > 1.0 at low temperatures compensates for reduced electrochemical activity; kt < 1.0 at high temperatures reflects increased capacity but reduced service life.