The battery in the photos is included in this sale. From the manufacturer:
"An extra long waterproof digital thermometer for the homebrewer. Take mash temperatures without lifting a lid and drop it down into your carboy for instant readings before pitching yeast. Excellent tool for mash tuns and carboys."
Specs from the manufacturer:
IP66/67 waterproof rating
24" inch heavy duty SS probe
Min/Max memory
Hold feature
Ideal for mash temp readings and carboys
C/F switchable
5,000 hour battery life