How long it lasts: four discharges and a gauge

Once the battery was readable, the real question remained: how long does it last? I unplugged the robot several times and logged the voltage every minute until it switched off.

The measurements

No.	Day	State	Start	Time until shutdown
1	1 November, night	asleep	6.57 V	about 3 h
2	2 November	awake, after 1 h asleep	6.40 V	about 1 h 35
3	3 November	awake	6.50 V	reference curve for the gauge
4	4 November, morning	awake	6.56 V	2 h 23
5	4 November, evening	awake	6.46 V	2 h 19

Awake, the robot lasts between 1 h 35 and 2 h 23, depending on the starting charge. Asleep, about three hours.

The gauge

The energy tile now follows two measured curves: one for the robot awake, one for the robot asleep. It picks one depending on whether the motors are holding their position.

The alert comes at 6.20 volts, announced about 29 minutes before shutdown. Checked on both discharges of 4 November: 33 real minutes in the morning, 26 in the evening. Below 6.25 to 6.30 volts, the curve is right within three or four minutes. Above, it overestimates by about seven minutes. Right within a few minutes is enough to decide when to plug back in.

Charging

• A full charge takes two hours at most.
• The charger voltage rises, then levels off around 7.43 volts after about 1 h 40 (97 to 103 minutes depending on the evening). It is the only steady marker I found.
• The green LED on the base does not mean “full”. It lights up very early, and stays green as long as the robot is plugged in.

The empty battery trap

On the evening of 4 November, after shutdown, the robot started rebooting on its own, again and again: head tilted, motors switching on now and then, missing from the network. A battery drained to the very end is no longer enough to start, so the robot tries again. Just plug it back in.

If you own one

Do not trust the green LED. Read the voltage, unplugged, and count on about two hours awake, a little more if the battery was really full.