Smart thermostat shows E13 and reports low battery even after new batteries are installed.

Safety first: Only handle batteries; do not open the device.

• Use correct batteries: Install fresh, high-quality alkaline AA batteries. Avoid rechargeable NiMH cells, as their lower voltage can trigger low-battery warnings.
• Inspect contacts: Remove the batteries and inspect the metal contacts inside the thermostat. If corroded or dirty, gently clean with a cotton swab lightly moistened with isopropyl alcohol. Allow to dry fully.
• Check spring tension: Ensure the spring contacts are not bent or collapsed. Gently pull them out a millimeter if needed to improve contact.
• Reinsert firmly: Insert the batteries with correct polarity and ensure they are fully seated.
• Reset device: Leave the batteries out for 2 minutes, then reinsert and check if the E13 code clears.