Only one wire
Back in grade school, one of the smartest guys I ever met surprised me when I realized he didn’t understand that electricity had to flow in a circuit. His assumption seemed to be that electricity poured in, did its job and left, like air and fuel through an engine.
It turns out not having a strong understanding of electrical circuits put my friend in good company. MIT graduates, according to this video, struggle to light a bulb with a battery and a single wire. The standard wiring diagram shows a circuit starting with one battery terminal, flowing through a wire to one terminal on the bulb, through the bulb, through a second wire back to the other battery terminal.
The MIT grads are challenged to create a circuit with the same purpose with only one wire. The trick is to touch one terminal of the battery to one terminal of the bulb and use the wire to connect the other respective terminals.
Imagine you are an engineer at a company that makes a million flashlights a year. If you could eliminate the cost of that one additional wire and the additional manufacturing step, say for a penny in cost, the savings per year would be $10,000 a year.
This is an example of SCAMPER – Eliminate, the elimination of a component or step that improves a product or reduces its cost. It also highlights how an idea that seems obvious in retrospect can defy imagination when the problem it solves first shows itself.
How about no wires?
The majority of cylindrical cells, such as AA and AAA “batteries” and the 18650 and 21700 cells used in Tesla cars, all have the positive terminal at the top and negative at the bottom.
Building 21700 cells (like those being manufactured at the Tesla Gigafactory, pictured) into a battery pack for a Model 3 Tesla or a Powerwall 2 involves soldering terminals to both the top and bottom of each cell. An alternative would be to make packs into which cells with both terminals at the bottom could be twist-locked into place, like a lightbulb. This would speed up both assembly and disassembly, albeit at the additional manufacturing cost of socketed battery buses. In addition, the top of the battery could be shaped for easy manipulation, perhaps with a hex end or a tab that can facilitate the twisting and indicate when a secure connection is made.