Recommended replacement cycle of the battery (Q6BAT) for the EcoWebServerIII (MES3-255C-EN, MES3-255C-DM-EN)is 3 years. Provided that battery life varies according to energized time ratio as below.

Energized time ratio	Guaranteed value
0%	13,700hrs, 1.57years
30%	19,100hrs, 2.18years
50%	25,800hrs, 2.96years
70%	40,000hrs, 4.57years
100%	43,800hrs, 5years

"ERR. LED" of Server section lights upon battery exhaustion. For inquiries on the replacement battery, contact the dealer where you purchased this product.
The backup battery built in the demand control unit of the device with demand control function (MES3-255C-DM-EN) is not replaceable. Where voltage of a battery for clock backup is dropped, consider to update the EcoWebServerIII (MES3-255C-DM-EN). Compensation for power failure for the battery of clock backup is cumulatively 5 years (battery life 10 years).
* Energized time ratio: ratio while power ON of the EcoWebServerIII.