The readings for devices are as reliable as the devices provide. The panel is receiving the data from the device. If a device hasn’t been signaling at all for a while then the battery level won’t be accurate.
One thing that often affects this is the fact that a device may experience signaling trouble from lower battery levels before hitting its hard low battery threshold. This is not uncommon especially for devices which already have limited range or rely on mesh repeaters like door locks do.
Sensors which have other factors like environmental attenuation are susceptible to the same thing. Replacing batteries is a step in troubleshooting offline status for this reason.