i recently used my nano v2 till the battery got empty. I wonder if there is a protection against deep discharging the lipo.

Hi tobey,
Yes the lipo battery has build-in discharge and overcharge protection circuit.

how low does the voltage of the battery go?

I can find no data to support your claim of the battery having built-in discharge and overcharge protection circuit. The battery is a Lithium polymer battery 353545, 470ma/h, with nominal voltage of 3.7V, charging voltage of 4.2V and discharged voltage of 2.4V; with a life cycle of 500.

This battery also has just 2-wires, so there is no PTC temperature sensing thermister involved either. The same battery is used in both Nano V1 and Nano V2. The only difference is that the Nano V1 requires a 2-pin connector.

Please cite the source of your information about battery built-in protection.

It would be irresponsible to post invalid safety information on this forum, so this issue needs to be resolved. Either the battery has self protection or it doesn’t. My search results lean towards no protection inside the battery. Until positive source citing of protection circuit inside the battery, all users should assume no protection. Perhaps Seeed Studio would clarify this issue as it pertains to the Nano V1. The Nano V2 has battery overcharge protection circuits inside the Nano itself, but the V1 does not appear to have such overcharge protection.