batteryInDays returns 0.0 on physical device. Bug?

I am using SDK 4.1.1, and building for a Venu 2.

Here is my code:

if (Toybox.System.Stats has :batteryInDays) {
    var stats = System.getSystemStats();
    var battery_days = stats.batteryInDays;
    _battery_days = battery_days.format("%.1f");
} else {
    _battery_days = null;
}

This works fine in the simulator. On my physical watch, it returns 0.0, even when the battery is at 97%.

Has anyone confirmed they can get a valid batteryInDays reading on a physical device? (Preferably a Venu 2, as that's what I have)