Today's batteries that are charged in mobile robots are mostly based on the century-old system of charging contacts at the end of springs, first patented in 1899.
Spring-loaded collector contacts (spring contacts) drag or hang below the mobile robot in use and have low ground clearance and narrow height tolerance because they must physically slide up a ramp on the base: If they are mounted too low, they touch the floor or hit the side of the pedestal. If they are mounted too high, charging contacts have weak spring pressure or have no contact at all. Over time, they also have a high wear rate because the charging contacts are constantly sliding across the charging surfaces.