Life time of integrated lithium battery CR2032-1VC 3V

MOX hardware
1

Hello,

What is the life time of the integrated lithium battery CR2032-1VC 3V ?

2

V mém Turrisu 1.1 šlape uz pátý rok…

I have Turris 1.1 and this battery started its fifth year.

3

Maybe a better question would be what the battery is used for, what would drain it?

Most simular equipement i know of, it is used to keep the clock running in case of a power outage. That doesn’t happen often. So the drain (apart from self deischarge) would be rather minimal.

Anywho, this source (https://data.energizer.com/pdfs/cr2032.pdf) speaks of a self discharge of 1%/year.

4

This router is intent to be used embedded in a device in environments where it is powered only few hours per day (less than 12hours), few days per week (less than 5days).

5

There might be also microcontroller(s) on the system that store configurations during a power cycle, least the TO features

PCA9538 microcontroller (16-pin CMOS device that provides 8 bits of General Purpose parallel Input/Output (GPIO) expansion with interrupt and reset for I2C-bus/SMBus applications)

6

Dug a little bit deeper in the schematics of the TO (https://doc.turris.cz/doc/_media/rtrom01-schema.pdf). The battery is drawn on page 15 (PWR_schematic) where it supplies Vbat. On the very first page you can see that Vbat is only connected to the CPU_schematic (and PWR schematic).

On the CPU_schematic (page 2) it supplies the CPU 88F6820 on pin RTC_AVDD.

According to (https://www.marvell.com/docs/embedded-processors/assets/marvell-embedded-processors-armada-38x-hardware-specifications-2017-03.pdf):

  • page 35 shows its as the “RTC quiet power supply”.
  • page 104/106 shows its voltage requirements
  • page 120 shows the max. power requirements as 1 microAmp

So as suspected it powers a clock in the CPU during powerfail. When this happens the current drawn from the battery is 1 microAmp max.
The CR2032 has a capacity of about 200 mAh (to 2.6 Volts). This would suggest a standby time of 200.000 hours (excl. self discharge and other effects).
This is more than 20 years! I wouldn’t worry to much.

Hope this help.

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