Voltage is the first number many experimenters measure, but it is only one part of battery performance. A cell can show an impressive open-circuit voltage and collapse as soon as a real load is connected.
Add a load
Measure the voltage across a known resistor and use Ohm’s law to estimate current. Repeat with different loads. The drop between open-circuit and loaded voltage provides clues about internal resistance.
Measure over time
Useful batteries must deliver energy for a meaningful duration. Record voltage and current at intervals and calculate approximate watt-hours. For rechargeable chemistry, repeat charge-discharge cycles and watch how capacity changes.
Look at the materials
Corrosion, passivation, leakage, drying, swelling and electrode damage can make an otherwise interesting chemistry impractical. Cost and availability matter as well. The best laboratory result is not necessarily the best product.
That is the spirit of the ProStackAI Project Lab: a device is not “better” because it produces one exciting reading. It is better when the measurements show a useful improvement under repeatable conditions.