Energy Cells

Version 2.4

This started out simply as an attempt at creating better tables for the blog. It has turned into a more detailed look at energy cells in Transhuman Space. Most of this is not needed for gameplay but the extra detail does help flesh out the background.

Page 140 of Transhuman Space 3^rd edition tells us one pound of batteries stores 1 kilowatt-hour (3,600 kilowatt-seconds or 3.6 MJ) of energy, has a volume of 0.02 cubic feet and costs $30. It then gives examples of common standardized energy cell sizes. These have the same names as the power cells described in other third edition rules. The sizes are similar, but not identical to, the energy cell sizes given in 3e Ultra-Tech, p.10-11. In Ultra-tech 3e the AA cell is ¹⁄₁₆" in diameter and ¹⁄₃₂" thick, 8,000 to the pound. The A cell is ¼" diameter and ⅛" thick, 400 to the pound. In the THS descriptions, they would be 2,000 and 2,000 to a pound. 3e Ultra-Tech gives dimensions for cells but the density varies for the weights given.

THS 3e also tells us that a pound of battery occupies 0.02 cubic feet. Using this figure gives energy cells that seem far bulkier than seems likely. The AA cell, for example, works out as equivalent to a cube of sides of more than 6.5 mm. This seems impractical for an energy cell that is intended for use in very small items such as the 1/20" (1.27 mm) nanobug (THS 3e p.154). It seems likely the author was thinking of UT 3e AA cells and not aware the figures he gave describe something larger. UT 3e AA cells are still bigger than a nanobot.

I will deal with the subject of energy cells for very small devices presently. I began experimenting with different values for volume. I tried making the AA cell the equivalent of a 3 mm cube, which works out as a volume/lb of 54 cubic centimetres. Interestingly, this is 0.0019 cubic feet. This makes me wonder if the figure of 0.02 was a typo and should have read “0.002”. Not remembering the nanobug description, I decided to make the AA cell a 2.5 mm cube, which seemed a practical shape for such a small object. This gives a volume/lb of 31.25 cubic centimetres (0.0011 cubic feet). The cell descriptions below are based on this. Dimensions given are approximate, and given in metric since this is more likely to be used in the THS-era. The positive end of the cell is of a slightly smaller diameter.

Size	wt (lb)	no. /lb	kWh	Dimensions	Cost
AA3	0.0005	2000	0.0005	2.5 mm cube	$0.015
AA2	0.0005	2000	0.0005	1.6 dia. x 7.8 mm	$0.015
AA1	0.0005	2000	0.0005	4.5 dia. x 1 mm	$0.015
AA-Flex	0.0005	2000	0.0005	4 mm square.	$0.015
A1	0.005	200	0.005	5.8 dia. x 5.8 mm	$0.15
A2	0.005	200	0.005	12.7 dia. x 1.2 mm	$0.15
A-Flex	0.005	200	0.005	12.5 mm square	$0.15
B	0.05	20	0.05	12.7 dia. x 12.7 mm	$1.5
C	0.5	2	0.5	27 dia. x 27 mm	$15
D	5	0.2	5	86 mm square x 22 mm	$150
E	20	0.05	20	86 mm cube	$600

The limited volume of devices likely to use the smallest cells suggests that more than one configuration of some types may be needed. The most common variety of AA cell would be a 2.5 mm cube with rounded corners. These are relatively easy to handle, although it helps to have tweezers. Bulk packs of AA cubes include a pair of plastic tweezers. AA cubes are also known as AA³ or just AA3s. The AA1 configuration is intended for thin devices. AA2 cells are used in the narrowest of devices and are relatively uncommon compared to the other configurations. AA2s are known as “pin cells” or by similar names.

A-size is also common in more than one configuration, one being a flat disc and the other a more compact “pill-cell” cylinder. I have changed the size of the A1 from 7 dia. x 4 mm to 5.8 dia. x 5.8 mm. An A cell holds the same energy as a typical 20th century 9V battery, which is twenty times heavier (0.1lb).

B cells are of similar size to a pistol cartridge case. A stack of ten A2s can substitute for a B cell in some devices. The many applications for B cells include powering electrolasers and shock gloves.

C cells are slightly over an inch in diameter and height. (Actually similar to the size of a modern 3/5 C cell!) In the first version of this page, C cells were 26 dia. x 30 mm. Equipment designed for larger or smaller cells often has an adapter for C cell operation or can be fitted with a plug-in adaptor. The plug-in adaptor has a holder for one or more C cells and a universal power connector. It plugs into a socket on equipment rather like a modern USB device does. The connector will probably be a micro-USB plug. Applications for C cells include powering laser pistols and rifles. A C cell has the same power as a TL7 12V car battery.

My original idea was for D cells to be 50 dia. x 80 mm. Ultra-Tech 4e suggests D cells are dimensioned similarly to a paperback book. This shape is more space-efficient. Suggested dimensions for a D cell are 86 mm square x 22 mm. This configuration is consistent with the statement that a D cell might be worn on a belt. It also allows four D cells to substitute for an E.

Originally I had E cells sized as 90 dia. x 100 mm. If fitted with a carrying handle it would resemble a small paint can. Ultra-Tech 4e describes E cells as “about the size of a backpack”, which does not work out, suggesting a volume much larger than four D cells. The E cell is now a round-cornered cube of about 86 mm each side. Many have a carrying handle, and this is usually detached when the cell is installed. Heavy power demands use multiple E cells, individual E cells being easier to handle than a single larger cell.

Non-rechargeable cells have the same sizes, weight and cost as rechargeable cells but store twice the energy. Thus a non-rechargeable A-flex holds 0.01 kWh, twice the power of a modern 9V.

Ultra-Tech 4e p.19 changes the weight of AA and A cells to reflect those in THS 3e but there are inconsistencies with other sizes, as noted already. More usefully, Ultra-Tech 4e also introduces adhesive, flexible energy cells resembling polymer postage stamps. These are used in THS-era clothing, smart labels, smart paper, and flexible, disposable items. Flexible cells may be rechargeable or non-rechargeable. AA and A flexible cells are the usual cost; other sizes are 4 times the normal cost and may be much harder to acquire. Multiples of flexible AA and A cells are usually used instead of other sizes.

THS 3e p.140 tells us AA to E cells are just some of the standardized sizes available. Ultra-Tech 4e also had the 200lb F cell! In GURPS Terradyne TL7 power cellls (batteries) were still in wide use, even in Luna City. Other size energy cells may be encountered but the range and sizes suggested here should meet most needs. 

Very small devices that cannot use any of the AA cells proposed here would probably use built-in batteries and utilize wireless recharging systems. Physically changing the batteries in every microbot is not really practical! Instead treat such devices as taking a charge equivalent to an AA cell.

(Blogger still screws up tables! A solution!)