Button Cell Battery, 80mAh, Silver Oxide 1.55V
From Amazon
VARTA Batteries Electronics V390/SR54 silver battery 1-pack, Battery in original blister pack of 1
Conrad Electronic
Varta Button cell SR54, SR1131 1.55 V 1 pc(s) 59 mAh Silver oxide SILVER Coin V390/SR54 Bli 1
BatteryUpgrade
Varta V321 / SR65 / 321 Coin cell battery (Amount 1)