The loggers come with a 3.6V non-rechargeable Lithium battery. The size is a 2/3 AA battery. You can also purchase a 1/2 size AA battery with the same voltage (shown in images) which will in most cases have a lower capacity and lifespan. To avoid the need for spot welding I would recommend getting a battery with pre-fitted leads.

The original battery is from Tadiran, model SL-561 and has a rated temperature ranger of -55 to 130 °C. These batteries are pricey but worth it in the long run. I have a logger that has a battery that is over 12 years old and still works!

The loggers can get very hot when left lying in the sun. It is recommended to use the same battery as a replacement as most other batteries have a much lower temperature range and will probably start leaking when the logger is left in the sun and the battery temperature range is exceeded.

Solder the new battery to the large solder pads. Make sure you don't reverse the polarity.