Depth of discharge

Depth of discharge describes how far down you take the pack before plugging it back in. Topping up at 80 percent is shallow; running until the robot dies on the rug is deep.

It has a big effect on how long a pack lasts. In Battery University’s figures, one common lithium chemistry delivers roughly 300 full drains, but around 2,000 cycles if only a fifth of the charge is used each time.

This is why a robot that returns to its dock often can outlive a pack that gets flattened daily, even with the same cells inside.