Libris is designed to trigger an audio alert if your battery is below 10% charge level.  Audio message will say "Charge your personal mobile responder now. Please place your personal mobile responder in the charger now".

If you charge the Libris but it is still below the 10% threshold of battery life, as soon as you pull Libris from the charger you will be presented with a low battery audio alert.

At 3% charge the Libris will automatically power off.