How much can it carry
Energy on board, and what carrying it costs in mass and in volume you then have to move.
Electrification
Everything that carries current and moves
A car, a drone, a lift aircraft, a boat and a truck look like five different problems. In the record they are one: how much energy you can carry, how fast you can put it back, and what the heat does while you do.
Why the shapes matter less than they look
A pack is a pack whether it sits under a floor, in a wing or in a hull. The cell chemistry, the way heat leaves it, the current the interface can take and the standard that governs that interface are the same four questions every time. What changes is which one bites first.
In a car it is usually charge time. In a drone it is mass. In an aircraft it is the reserve you must still have when you land. In a boat it is what the water does to the cooling. Knowing which one governs your design is most of the first month, and it is readable long before it is buildable.
The order in which they bite is also the order in which they get expensive. A cell chosen badly is a purchase order. A thermal path designed badly is a redesign. A charging interface aimed at the wrong standard is a product that works and cannot be sold.
01. The car
The motor is solved. The heat is not
Permanent magnet machines and the inverters that drive them are mature, well documented and available from more than one supplier. That part of the record is thick and mostly settled.
What still ends projects is what happens between the cell and the air: the path heat takes out of the pack, and whether the charging interface you designed against is the one the market will have when you ship. Both are in the record, filed by people who found out the expensive way.
02. The drone
Every gram is paid for four times
A gram added to a rotorcraft is paid in structure, in the motor that has to lift it, in the cell that has to feed that motor, and in the structure that has to carry the bigger cell. That loop is why drone projects converge slowly and then all at once.
We read the mass loop before the first frame is cut, and we read what the airspace rules will require of the payload you are planning. A camera that needs a certification you did not budget for is cheaper to find in a document than in a flight test.
The loop closes faster than most teams expect. On a small airframe, a hundred grams of added payload can cost three hundred grams of take off mass by the time the structure has caught up with it.
03. Lift aircraft and helicopters
Hover is expensive and cruise is cheap
A rotorcraft spends most of its energy standing still in the air. A wing spends most of its energy going somewhere. Every lift and cruise design is an argument about how long you have to do the first before you are allowed to do the second.
The transition between them is where the patents are dense and where the certification path is least settled. We map both before a configuration is chosen, because changing configuration later means starting the aerodynamics again.
04. Electric aircraft
The reserve is the design
A battery aircraft must land with energy it was never allowed to use. That reserve is written into the rules, it does not shrink because the flight went well, and it is the single number that decides whether a route closes or opens.
05. Electric boats
The water is a gift and a problem
A hull sits in the best coolant a vehicle could ask for, and in the most corrosive environment a pack could be put in. The first fact makes thermal design easy. The second decides how long the boat lasts.
Displacement hulls reward efficiency in a way road vehicles do not, because the power needed rises sharply with speed. A boat designed around the speed it actually travels at is a different boat from one designed around its top speed.
06. Trucks and trains
Two answers to the same question
A train solved the energy problem by never carrying it: the wire is above and the pantograph reaches up. A truck carries everything it needs and then has to put it back faster than anyone finds comfortable.
Both roads are open for heavy transport and both have a record worth reading. Which one fits depends on the duty cycle, and the duty cycle is measurable long before a vehicle exists.
The drawings
What we draw while we read
Every engagement leaves a set of drawings like these. It is how a claim, a standard or a measurement becomes something a team can argue about in a room.
07. Making the part
Printed and laid up, not machined from a block
Additive manufacturing changed which shapes are affordable, and composite lay up changed which shapes are light. Together they moved the constraint from what a machine can cut to what a part can be asked to do.
Both bring their own failure modes, and both are well covered in the record: layer adhesion in one, fibre direction and the resin system in the other. A prototype that fails at a layer boundary fails for a reason someone already wrote down.
Neither replaces machining. What they do is move the decision earlier: you now choose the process while the part is still a sketch, and that choice sets what the part can weigh and what it can cost.
08. What the vehicle owes
A battery starts the race behind
Building a pack costs something before the vehicle has moved a metre. An electric vehicle therefore begins with a debt, and pays it back over distance. Where the two lines cross depends on the cell, on the grid that charges it, and on how far the thing actually travels.
That is an argument that should be made with a measurement and not with a feeling. What the pack is worth after the vehicle is done with it belongs in the same calculation, and it is usually left out.
The four questions
Asked of every one of them
Whatever the shape, the first month asks these. The answers differ. The questions do not.
How fast can it be filled
The interface, the standard that governs it, and the curve that decides what the number on the poster really means.
Where does the heat go
Out of the cell, through the structure, into air or water. The path is the design, and it is decided early whether you decide it or not.
What happens after
Second life, recovery, and what the pack is still worth when the vehicle is finished with it.
The field
Six places the current already runs
None of these is a prototype. They are all in service somewhere today.
Bays marked for electric vehicles, where the queue is for the connection and not the space. A trolleybus, which solves the battery problem by not having one. 
Overhead line across a crossing. The oldest electric transport still carries the most. A solar electric passenger boat, where the water both cools and corrodes. A solar aircraft on a lakebed, built around an energy budget rather than a cabin. Wind turbines, which decide how quickly a battery pays back what it cost to make.
Something in this list is yours
Tell us which one and what worries you about it. If the record says it is taken, you will hear that on the call.