2.0 Supra back up accessory battery under the hood - replacement?

[BMW_GHOST_INSIDE]

Has anyone had to replace the secondary back up battery under the hood? The one used for accessories. Not the main battery in the trunk. How long do they normally last. My 2.0 is a year 21 and was wondering how long will it live until needing replacement. I just replaced the main batery in the trunk today and hads it programed. Now, wondering if the secondary battery will need replacement too?

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