‘LO’ means low temperature, and not low battery – so no worries!
The reason why the thermometer shows ‘LO’ from time-to-time is that room temperature is roughly 69.8°F/21°C), which is too low for our basal thermometer (which can only measure down to 89.6°F/32°C). Please make sure to place the thermometer as far back as possible in your mouth and underneath your tongue, right at the root of your tongue, then close your mouth tightly before you turn it on to avoid the thermometer showing LO.
Basal body temperature should be around 96.3-98.4°F/35.8–36.9°C degrees. Any higher than this, then you probably have a fever and we, therefore, advise you to mark your reading as a 'Deviating temp.' due to 'Sick / On medication' so that the algorithm disregards that reading. 
Order one basal thermometer from our webshop today!