1. Battery protection circuit: Most lithium batteries have built-in protection circuits to prevent over-discharging and over-charging. When the battery charge drops to a very low level, the protection circuit usually cuts the battery's current to prevent further discharge, thereby protecting the battery from damage.
2. Battery hardware damage: If the battery has been working in an over-discharged state for a period of time, it may cause damage to the internal components of the battery, such as the electrolyte in a lithium-ion battery. In this case, even if the battery is charged, its normal function may not be restored.
3. Safety considerations: Lithium batteries in extremely low voltage state have the risk of explosion and fire. To be safe, chargers and battery management systems generally avoid attempting to charge a battery in this state.
If you're having issues with your battery going to zero and won't charge, here are some suggestions:
1. Use specialized charging equipment: Some equipment specially designed to restore very low voltage lithium batteries may help. These devices are often capable of restarting the battery at very low current and voltage to bring it to a chargeable state.
2. Ask a professional to help: If you are not sure how to handle an extremely low voltage lithium battery, or for safety reasons, it is best to ask a professional to handle it, they may have the experience and equipment to handle such situations.