thermometer life

How long does a thermometer battery generally last? I had a feeling my thermometer was playing up this morning as it keeps giving me different temps. ie If I take temp 3 times, with exactly the same placement, it will give me 3 different temps, all way different.

I went out today to get a new battery and couldn't find one, so I bought a new thermometer (cant live without it) This one is taking my temp at least 0.12 degrees higher than my old one.

Should I continue using my old one for the rest of this cycle, then swap to new one next cycle (hopefully I wont need it) or is it OK to just use the new one now?

I am in a bit of a dilemma, because if my old one is playing up my temps will be wrong and mess up my chart, but if I change to the new one that could mess up my chart too.

What to do???

If it was me i would change it depending how far i was into my cycle, like if i was in AF i would change it but if it was coming up to ovualtion or past it i wouldnt want to change it. But i was also curious to see how long they last for :)

Well I have done some research and supposedly they last for about 2 years! I am just going to finish this cycle off using the old one then swap to the new one next cycle if I need too. I am also thinking about temping vaginally next cycle as I don't feel like I get the thermometer placement right.