Were going to run around the other side of the table and ask the Q again.

A bank of storage batteries ( forget auto ) has run low, it's now time for them to be recharged. What is the sensor ( device ) that recognize and kicks in the charging. Is it a charge controller ?

T.D.

That's about the best description, but "battery charger" is usually sufficient. "Chearge controllers" are generally a bit more sophisticated ans used with electric cars and alternative energy. It may have to know whether to charge the batteries or dump to the grid or the house. Maybe even select utility, battery, wind or generator power.

Charing algorithms are different based on battery chemistry. Temperature sensors are often employed to avoid overcharging.

Laptop batteries are outfitted with a "battery gas gage" This thends to look at energy in and out. That why you have to calibrate a new battery. Volage is generally not a good indicatior of state of charge. When it's used, overcharing can result.