# Is power of a battery constant?

In my question I'm neglecting the impact of discharging.

I'm trying to make sense of Watt's law: $$P=IV.$$ I always thought that the voltage and the power of a battery were constant features that reflected the strength of the chemical forces inside the battery. As for the current, I thought that it was determined by the voltage as well as the arrangement of the circuit. Now, from Watt's law, something about this view must be wrong, as according to it current varies from one circuit to another, whereas voltage and power don't. I suspect that it must be something about my understanding of what the power of a battery is. So could someone explain to me what the power of a battery is and what it tells me about the circuit and the battery? Is it constant for a given battery, or does it vary from one circuit to another? Thank you all!

• This may help. Commented Jan 18 at 18:11
• Some people call this a battery: amazon.com/dp/B091BSG9GS But, it actually is much more. It is a combination of a battery, and a "smart" charger for the battery, and a switch-mode power supply that provides a regulated (constant) 5V to an external device, even as the voltage of its internal battery decreases with the state-of-charge. "Batteries" like that sometimes are labelled with a capacity in Watt hours. Is that the kind of battery you meant? Or, did you mean something more like this? amazon.com/dp/B00MH4QKP6 Commented Jan 18 at 22:40