Bottom line
Choose endurance and retention at the actual operating temperature, not the 25 °C headline. Then decide how much logging belongs in external EEPROM versus internal flash.
What actually gets stored
- State of charge, state of health and learned parameters.
- Fault and event logs with timestamps.
- Pack history: cycle count, accumulated charge, service records.
- Calibration and binning data written once at end of line.
Endurance at temperature
Endurance is usually specified at a defined temperature, often 85 °C or 125 °C. A part rated for 4 million cycles at 25 °C can be rated far lower at the temperature inside a battery pack.
Retention is temperature dependent
Retention figures quoted as “100 years” apply at 25 °C. At 125 °C the same device may retain data for a much shorter period — the datasheet retention-versus-temperature curve is the document to read.
External EEPROM or internal flash?
| Aspect | External EEPROM | Internal flash |
|---|---|---|
| Endurance | Higher, specified separately | Lower, shared with program memory |
| Write behaviour | Byte/page write, no code stall | Writing may halt execution |
| Cost and area | One extra part | No extra part |
| Failure isolation | Data corruption does not brick the MCU | Corruption can affect firmware |
Related products
| Part number | Brand | Package | Qualification | Operating temperature | Key parameters | Docs | Actions |
|---|---|---|---|---|---|---|---|
| AT24C64D-SSHM-T In stock | Microchip | SOIC-8 | AEC-Q100 Grade 1 qualified | -40 °C ~ +125 °C | density: 64 Kbit · iface: I²C · vcc: 1.7 ~ 5.5 V | Datasheet ↗ | |
| MKE04Z8VWJ4 In stock | NXP | SOIC-20 | AEC-Q100 Grade 1 qualified | -40 °C ~ +125 °C | core: Arm Cortex-M0+ · freq: 48 MHz · flash: 8 KB | Datasheet ↗ | |
| 24LC256-I/SM In stock | Microchip | DFN | Qualification to be verified | To be confirmed | To be confirmed | Datasheet ↗ | |
| AT24C02C-SSHM-T In stock | Microchip | SOT23 | Qualification to be verified | To be confirmed | To be confirmed | Datasheet ↗ | |
| AT24CM01-SSHD-T In stock | Microchip | SOIC-8 | Qualification to be verified | To be confirmed | To be confirmed | Datasheet ↗ | |
| AT93C46DN-SH-T In stock | Microchip | SOIC-8 | Qualification to be verified | To be confirmed | To be confirmed | Datasheet ↗ |
Related applications
FAQ
Do I need to back up the data?
For SOC and fault logs, yes — store two copies with a sequence number or checksum so a write interrupted by power loss can be detected.
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Source：Manufacturer EEPROM datasheets; FASTSPEED internal selection notes.
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