HP 35s HP 35s scientific calculator - User Guide - Page 289

Changing the Batteries The calculator is powered by two 3-volt lithium coin batteries, CR2032. Replace the batteries as soon as possible when the low battery annunciator ( ) appears. If the battery annunciator is on, and the display dims, you may lose data. If data is lost, the message is displayed. Once you've removed the batteries, replace them within 2 minutes to avoid losing stored information. (Have the new batteries readily at hand before you open the battery compartment.) To install batteries: 1. Have two fresh button-cell batteries at hand. Avoid touching the battery terminals - handle batteries only by their edges. 2. Make sure the calculator is OFF. Do not press ON (  ) again until the entire battery-changing procedure is completed. If the calculator is ON when the batteries are removed, the contents of Continuous Memory will be erased. 用 BK+B 3. Turn the calculator over and slide off the battery cover. 4. To prevent memory loss, never remove two old batteries at the same time. Be sure to remove and replace the batteries one at a time. Support, Batteries, and Service A-3