The indicators of a fully charged lead-acid cell include:

1. Stable specific gravity: The specific gravity of the electrolyte in a lead-acid battery will stabilize when the battery is fully charged.
2. Open circuit voltage: A fully charged lead-acid battery will have an open circuit voltage of around 2.1 volts per cell (12.6 volts for a 12V battery).
3. Visual inspection: Some lead-acid batteries have built-in indicators, such as a color-coded hydrometer or a built-in charge indicator, to show when the battery is fully charged.

It’s important to note that these indicators may vary depending on the specific type and design of the lead-acid battery. Always refer to the manufacturer’s guidelines for the most accurate information.