Button Cell Battery, 39mAh, Silver Oxide 1.55V
From Amazon
Varta V329/SR731 Silver Oxide Button Cell Watch Battery – Pack of 1
Conrad Electronic
Varta Button cell SR731 1.55 V 1 pc(s) 37 mAh Silver oxide SILVER Coin V329/SR731 NaBli 1
BatteryUpgrade
Varta V329 (SR731SW) Coin cell battery (Amount 1)