The predecessors to the 60 CT series flashes were the 202 and 402 flashes. They came standard with either a liquid electrolyte battery or a nickel cadmium battery. Unlike Ralph, I've had lots of use of liquid electrolyte batteries in those flashes. And the early power packs for the 60CT series flashes did have a switch position for them - labelled as lead acid if I recall correctly.

When the Dryfit batteries became available for the 60CT series flashes it was very convenient because they would work with the power packs for the 402 and 202 flashes - as long as you didn't try to charge those batteries with those power packs.

There is a third type of battery that some people are using, but Metz doesn't support. It is a lithium-ion battery. It cannot be charged in the Metz power pack or with the Metz wall plug chargers. It may be that you have one of them.

EDIT: here is a link for one of the lithium-ion batteries: http://www.sabahoceanic.com/epages/s...Products/A0116