Layer Cells
Zinc Carbon Prismatic, Mini-max, Batrymax and PowerPack
From the 1940s a "layer type" biscuit cell was used for HT or "B" packs. From the mid 1950s it was used for Transistor radios, mostly 9V, or 6 cells. At lower currents the capacity is much higher and also it fits a rectangular or square space with less voids also decreasing size or increasing capacity. The internal resistance is much higher so they are unsuitable for high current drain like tube filaments, lamps or motors. The USA Eveready may have first developed them for small HT packs of the 1940 Personal Radio sets which didn't appear in the UK till 1946/1947 (Romac, Ever Ready, Vidor and Marconiphone/EMI).
A PP9 pack is about 5000mAH at 20mA and takes the same space as made from 6 x B cells which are just over 2500mAH at 50mA. Actually some European Transistor sets can take 2 off 3R12 (Old Ever Ready 1289) packs or a PP9.
For the PP3 the layer pack is about 460mAH or more at 12mA. But the Alkaline is only 590mAH at 12mA because the 6 LR61 cells waste space compared to the Layer cells. Since at best the Alkaline costs twice as much it's poor value compared to layer type. In contrast since the regular cylindrical Alkaline is x2.4 to x3 life of Zinc at low current draw, the Alkaline as long as no more than x2 price are better value.
(Left: Eveready minimax layer cell)
As a comparison the 6F100 (PP3 9V) is about 4500mAH for a transistor radio and 6 off "B" cells (R12) take the same space but are about 2000mAH for a transistor Radio but 2500mAH for 9mA HT. The F100 cells used in a 90V pack at 9mA will be about 5000mAH, so a big space saving. if a 2500mAH flat or prismatic cell is used. But in a motor driven or bright torch the 6F100 might be only 900mA and the R12 cells about 1800mAH. Due to the double capacity of Alkaline vs Zinc Carbon at low current draw, space can be "wasted" using close fitting Alkaline cells instead of layer types but the capacity increase is only 15% to 25% not the 200% of Alkaline vs Zinc Carbon or Zinc Chloride.
The Battery Valve (Tube) HT of 1940s to 1959 was 45 V to 90V and 5mA to 12mA depending on model. Prior to the Layer cell almost all HT packs are 30 to perhaps 134 "B" size cells, some used "AA" sized cells. 1.5V LT packs used two to eighteen off D, E or F cells in parallel. The largest US battery pack used 24 F cells as 4 paralleled sets of 6 for 9V (Eveready 716). The highest voltage pack used 336 layer cells for 510V (Eveready 497). The UK Ever Ready / Lissen All Dry Portable of 1939 was one of the earliest UK portable radios without a Lead Acid Accumulator. The 1939 Ever Ready 5124 / Lissen 8515 etc used the AD3 Combo pack (probably first use), the AD3 would have been 60 off "B" cells in series for 90V and 8 off "F" cells as this for just over 0.9V end point per cell on the HT pack and 1.0V end point on the LT gives the same life assuming approximately 250mA LT and 8 to 11mA HT, or close to 250 hours for 10 Shillings in 1939. Compare with SIX hours on some DAB radios! Of course it's a large battery pack!
In 1954 "Radio and Television Reference Book", (Gen Ed. Molloy) it's claimed a layer-built battery pack is about 2/3rds weight and 1/2th the volume for the same capacity. Also mentioned is the Valve Manufacturer's recommendation that the LT pack should be 1V per cell when the HT pack is totally exhausted (stated as 0.75V). In general the DK91 / 1R5 (the original Miniature All Dry tube) operates only down to 1V as mixer/oscillator.
Most of the later 1950s Transistor Power Packs (PP3, PP7, PP9 etc) appear to use the same layer cells as the older HT packs. Capacity reduces dramatically at higher currents as internal resistance is high. The longest life pack for a 9V transistor set was the PP10 using a two pin connector rather than snaps.
There are not "Zinc Carbon" and "Zinc Chloride" versions. There are Alkaline, NiCd and NiMH rectangular cells in rectangular cases but other than "naked" PCB NiMH these are now very rare. In practice all Alkaline and most NiMH replacements of layer pack use button, coin or cylindrical cells. The 6LR61 Alkaline may give only 14% to 20% extra capacity compared to Layer 6F22 as it's 6 off cylindrical LR61 cells (similar to "AAAA", size, perhaps 1.5mm shorter) but has a longer shelf life and less "droop" in discharge vs time hence superior for Smoke alarms but poorer value to make 45V to 120V "HT" packs.
US Eveready / NCC called the layer type pack "mini-max" and UK Ever Ready "Batrymax". Only the 6F22 (9V PP3) is now commonly available though the 6F100 (9V PP9) is still produced