Alix2D3 or Alix2D13 - What difference does the RTC battery make in pfSense?

  • Hi everyone,

    I noticed that PC Engines has two types of the Alix board that are very similar except for one includes RTC battery and the other doesn't have the option for that.

    1- Do I have to purchase Alix2D13 to use it with pfSense + SD Card? or is the RTC battery (function) not needed at all for my situation?
    2- What purpose does the battery serve on this board for usage with other software than pfSense?

    It's not the $1 that I save but rather the headache of changing the battery 3 years down the road which makes me not want it. So, if I can avoid it, I will want to avoid it.


  • You should check with PC Engines, but I expect the cell is a BACKUP power source for the RTC. Hence if the mother board gets adequate power cell drain will be nil and the cell should last last close to its shelf life, which I believe is considered to be around 10 years for a typical lithium coin cell.

  • So, let's say the battery runs out, how does that effect pfSense? does it at all? What complications could this cause?

  • Assuming the battery provides backup power for the RTC then battery exhaustion has no effect on pfSense until the system loses power THEN on the next restart the date/time will be wildly wrong until ntp is able to correct it. While the local date time is wrong timestamps in log messages will be wrong, file time stamps will be wrong, scheduled firewall rules will "misbehave" etc. FreeBSD is unlikely to care but you might care if you have to use timestamps for some sort of diagnostic purpose or incremental file backups etc.

  • Thanks Wallybob. Indeed this is confirmed by PcEngines techs:

    "The only difference is the missing battery and pin-header.
    If you plan to use pfSense which uses an NTP to sync time, you don't need the battery and the alix2d3 is fine."

    So, I am assuming that as long as there is internet and I am not using any scheduled or cron jobs then I should be fine. Even if I am using this, it won't "BREAK" the system but it might give me different behaviour.

  • FWIW, i previously had a WRAP board (without RTC battery backup) and i dearly missed the RTC backup. After a power cycle, for whatever reason (usually the kids' way of resetting), sometimes the network timesync did not work (don't know why). In these cases, i had to change the timeserver pool settings for it to reconnect. Without the correct time, the schedules where of and some members of the family did not have internet because of this. I now have the ALIX 2D13 and this problem is gone.

    BTW, i didn't change the board for this reason, but because my good old WRAP died.

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