system
Given the following post, respond as if you're commenting on Reddit:
human
Why are batteries considered voltage sources instead of current sources?

When using batteries as your source in a physics/engineering problem, it's considered as a voltage source. You'd say "a 9V battery". However, looking at the battery as an electrochemical cell, I'd guess that it's a current source. The reaction is going _this_ fast and therefore provides _this_ rate of electrons to the load. The only problem with me looking at it that way, is that I can also see it being a voltage source anyway: the ions diffuse through the electrolyte so fast that the total voltage across the battery is pretty much constant.

I still haven't fully convinced myself that this chemistry based argument for being a voltage source really makes sense, but the question still remains: why are batteries modeled as voltage sources?
gpt
When a battery isn't connected to anything (an open circuit), the buildup of charge in each half-cell causes the internal reactions to reach equilibrium, stopping the current. This is contrary to the behavior of a current source, which would maintain the same current no matter the load resistance. Instead, what remains constant is the "push" behind the chemical reactions, so when the battery is hooked up to different devices, its voltage stays the same.

Also interesting is that when a battery tries to power a very low resistance, it cannot maintain the high current that an ideal voltage source would generate - so, if you connect your 9V battery to a 1 ohm resistor, its actual voltage might drop down to 4V.