7.4V Li-Ion minimum voltage

Hello mates,

I am designing a mobile robot and for the power supply I have chosen a
7.4V Li-Ion battery (originally for JVC VCR).

From what I have read so far, it seems that it is important not to let
the Li-Ion battery voltage fall below a certain level, because it

damages the battery.

My question is, then, what voltage threshold should I chose for
monitoring?

Cheers,
Alexiey