This is copied from the current 60 CT1 manual:

"2.2.1 Charging the battery
The 60-38 rechargeable battery must only be charged with the battery charger
(Table 2, Page 513). The operating voltage must be set on the battery
charger prior to the charging operation.
Note ! During charging the flash unit must be turned off !
Recharging an exhausted battery to 80% of its capacity takes approx. 7 hours.
During this time, the red monitoring light  remains illuminated. As
soon as the battery has been recharged up to 80% of its capacity the red
monitoring light  starts flashing. The green monitoring light  (fig. 5)
remains illuminated during the whole recharging procedure. After a further
six hours the accumulator is then fully charged
The battery is exhausted when recycling after a full-power flash takes more
than 30 seconds. An exhausted battery must be immediately recharged."

For some reason, there doesn't seem to be anything similar in the current CT4 manual about how to charge the battery.