Eveready No. 770 - 45 Volt 'B' Battery
1936/37 version. The first series to have a female pin receptacle for electrical connections.
Photo below shows a plug adapter that Eveready made to work with regular battery cables.
My Atwater Kent model 768 of 1935 vintage and a complete set of batteries to power this set. The Eveready Air Cell filament battery was rated for about 1000 hours of service - the presumed yearly use of the radio. The total cost of these five disposable batteries was about $22.50. The CPI Calculator says that this is now equivalent to about $358.
There is no mistake here.... The AK 768 represents the maximum performance for an Air Cell rated design.
There are four 45 Volt batteries in series with a tap at 22 1/2 Volts to provide the 'C' bias. The Type 30 output tubes, run in push-pull, were being driven pretty much at their maximum ratings with up to 160 volts on the plates.
I can send you the scan for this battery artwork. It is a large file best printed out on a large format ink jet printer.