Electrical – this flex pcb connector called?

You are likely looking for bullet or barrel connectors. Try going to digikey in the terminals sub section : http://www.digikey.com/product-search/en/connectors-interconnects/terminals-barrel-bullet-connectors/1442843?k=bullet

Another source would be http://www.digikey.com/product-search/en/connectors-interconnects/rectangular-connectors-contacts/1442670?stock=1

These would be crimp on (can be soldered) to wire, providing you a single barrel like connection. You will need to use the search functionality to sort out what you are looking for specifically. I would use molex for the manufacturer as they make an assortment of female connections for power, such as what you would see on vintage RC car battery packs. Just search google images for "rc battery pack connectors".

Thanks to a comment from Nick Alexeev (above, in comments), I realized that I had managed to check Mouser, Jameco, etc. but neglected to check DigiKey (of all places).

It appears that this part is one of the Molex Easy-On™ 503555 series connectors; specifically the 5035664300. Taking a look at the datasheet, the flex side of the connector also matches the description (staggered contacts).

Thanks for taking a look, folks!