Thanks Bill / batterymaker1
I've decided the problem is partly philosophical than engineering.
I can make and pack boxes and fill them entirely with batteries or partially and put inverter(s). I've even considered a pair of 12V 7AH Lead Acid Gel, or 1 x 12AH Lead Acid Gel (11.5V parallel via diodes, 24V or straight 12V).
Suitcase is strong tan leather and 45+ years old and looks about 5 years old. Used by my Grandfather as a lunch box when he went fly fishing.
Internal size is 11 x 23.5 x 37.5 cm (4.25" x 9.2" x 14.75"), with inside of lid rest on edge when closed.
I have a nice 8" speaker and printout correct scale of pye sunrise+ clouds (that I will cut with my router).
I thought it would be nice to use a real (though rechargeable) replica 1950s battery pack(s) for my imaginary alternate past 1950/1960 Russian sub-miniature valve powered radio receiver/transmitter.