When your APC Smart-UPS starts showing "Connect battery" warnings despite reporting 100% charge, it's time to pay attention. The sulfur/rotten egg smell is a classic indicator of battery failure - specifically, hydrogen sulfide gas released during lead-acid battery decomposition.

You did right by ventilating the area and powering down the UPS. Hydrogen sulfide is toxic and flammable. Here's what else you should do:

1. Isolate the UPS from network equipment
2. Wear gloves when handling the battery
3. Check for visible leaks or bulging

The swollen battery in your photo confirms catastrophic failure. Replacement is straightforward:

# Sample battery check script (Linux)
#!/bin/bash
ups_battery=$(apcaccess status | grep "BCHARGE")
if [[ $ups_battery == *"100"* ]]; then
    echo "Warning: Possible false battery reading"
fi

Implement these monitoring solutions:

// UPS monitoring snippet (Node.js)
const apcupsd = require('apcupsd');

apcupsd.status((err, data) => {
  if (data.batteryCharge > 95 && data.loadPct > 50) {
    alertAdmin('Potential battery calibration issue');
  }
});

If you see:
- Multiple swollen batteries
- Corrosion on terminals
- Persistent sulfur smell after replacement
Contact APC support immediately as this may indicate charger circuit failure.

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When you detect that distinctive rotten egg odor in your server room, it's almost always one culprit: failed lead-acid batteries in your UPS system. The smell comes from hydrogen sulfide gas released during battery thermal runaway.

// Sample UPS status interpretation
if (errorState === "Connect battery" && batteryPercentage === 100) {
  console.warn("Potential battery communication failure");
  initiateBatteryCheck();
}

The "Connect battery" warning at 100% charge suggests the UPS can't properly communicate with the battery pack, often preceding failure.

• Immediate power down - You've done right by shutting down the UPS
• Ventilation priority - Hydrogen sulfide is toxic at high concentrations
• Visual inspection - Look for bulging/swollen battery cases (as seen in your photo)

For sysadmins managing multiple UPS units:

#!/bin/bash
# UPS battery health monitor
APCACCESS_OUTPUT=$(apcaccess status)
BATT_STATUS=$(echo "$APCACCESS_OUTPUT" | grep "BATTSTATUS" | awk '{print $3}')

if [ "$BATT_STATUS" == "FAILED" ]; then
  echo "CRITICAL: Battery replacement required" | mail -s "UPS Alert" admin@example.com
  systemctl poweroff # Safely shutdown connected equipment
fi

1. Implement SNMP monitoring for UPS units
2. Replace batteries every 3-5 years (sooner in hot environments)
3. Consider lithium-ion replacements for critical infrastructure

If you observe:

• Visible battery leakage (acid corrosion)
• Multiple failed battery units
• UPS won't power on after battery replacement

These indicate potential motherboard damage requiring APC-certified repair.