Smart battery syndrome

[Circlotron]

My camcorder has a smart battery and if I don't use it for a long period of time it discharges somewhat. I turn the camera on and it might say 10 minutes of battery time available. I let it run and after a short time the low battery logo comes on but it might still run another hour before it finally goes off.

I can understand if the battery was lower than indicated because is has discharged without that current going through the gas gauge circuit, but why should the battery be better than indicated?

[Kilrah]

Do you leave your battery in the device?

If yes the battery doesn't discharge because of its own smart circuitry, but because the attached device draws some current. It goes through the gauge circuit, but the circuit just can't measure such small currents accurately so accumulated error may be huge in one way or the other.

The circuit could also be assuming a battery self-discharge rate much higher than what it actually is.

[Circlotron]

Do you leave your battery in the device?

No, I always take them out. I have a large and a small battery and they both do the same thing.
It's a Canon Legria HF G10, almost identical to the HF G20(?) Dave was using to make his videos up until recently, so it's not a cheap and nasty camera but something that you would expect to be properly engineered.