system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are rechargeable batteries only 1.2V?

A lot of devices expect 1.5V batteries and report 1.2V rechargeables as empty sooner. Wouldn’t it be better to make rechargeables 1.5V as well? What is preventing that to happen?
gpt
The voltage generated in a battery is due to specific chemical reactions between the electrodes and the dielectric. This is more or less predetermined by what the battery is made of. 

There are other features more important in a battery - safety, reliability/rechargeability, size and energy density, current carrying capacity, cost etc. Modern commercial batteries have to optimize the above. The voltage is a very very minor issue ultimately because voltages are easily and efficiently adjusted by external circuitry. There is essentially no point to making a battery $10 more expensive just to try to eliminate $1 worth of external circuitry.