I wonder why is there no standard for Lithium ion batteries especially for portable devices,we can easily have a standard dimension/fit for similar capacities and power rating imposed by IEEE or similar organisations. In this way we can use the ones of older mobile phones which do not comply to current protocols of 4g/5g in other equipments like music players.. If we have standards for USB ports/bluetooth/wifi technology we can have for this too! On top of that devices dont have a simple cover to dismount the battery nowadays!
tl; dr version: market needs and safety concerns are different for Li-ion vs. primary cell (e.g., alkaline) types.
The beauty of standards is that there are so many to choose from...
Li-ion cells do come in some standard sizes, such as the well-known 18650 that's used for laptop battery packs, R/C models, drones, and even electric vehicles.
That said, Li-ion cells pose both a challenge and an opportunity compared to older battery technologies.
- challenge: safety (under / over/ reverse polarity) protection
- opportunity: prismatic cells for thinner / smaller devices
Because of the number of accidents with Li-ion cells in the field, battery makers are increasingly reluctant to sell them to individuals unless the cells have built-in protection. This market, while important, is troublesome owing to its liability. So there's less incentive for them to make a wide variety of form factors for every market niche.
(there's lots of YouTube videos of idiots who've 'modded' their vape pods and have had their batteries explode. I'll leave that to you, dear reader, to find. It's nearly as entertaining as Russian dashcam videos.)
On the other hand, for large OEM buyers of batteries (like phone manufacturers) who have known expertise in battery safety, it is worth making custom prismatic batteries for them to fit their product. And in fact, major, vertically integrated phone makers like Samsung and LG manufacture their own for internal consumption.
Standards are developed and agreed by companies to make it easy for end users to have interchangeable or interopearable parts, like light bulbs or AA batteries or headphone plugs and sockets. Internal components which are not accessable without screwdrivers, soldering irons or heat guns are not considered to be accessible by end users, only by service technicians since they need to use particular tools and skills. There is little incentive for manufacturers to co-operate on standardisation work for internal components, and a high incentive for them to design custom parts.
There is always some trade-off when using standardarized parts that they may not be optimal in all aspects for the application. Since everyone wants their battery life to be as high as possible, the manufacturer has the incentive to fill the available space with the battery, not just to be forced to choose the existing battery with the nearest size to what they can fit, and waste the remaining space.