Lithium-ion batteries don't like heat. High temperatures increase internal resistance, which drains the battery faster. So in summer, you'll notice your disposable dies quicker than in winter. The catch? If you try to cool it down in the fridge, condensation can get inside and damage the electronics. The better move is to avoid direct sun and hot cars. If you're using a rechargeable model like any of the VERTEX series, keep it out of the heat while charging. Room temperature is your friend.