That may or may not actually damage the battery, depending on the brand/quality of battery. But it is too low to allow most chargers to work. Most chargers give an error if any cell on the battery is below 3 volts (9volts total for a 3cell battery). So if your battery gets drained below 9 volts total, your charger may not want to charge it. I would recomend getting an esc designed for lipo's or get a programable esc.