The CR2032 Lithium battery that backs up the real time clock of a Keithley DMM6500 lasts 18 months. Here's how to replace it. The reference manual says the battery is not user replaceable. This post on EEVblog, by Shodan from Russia, shows it's not difficult, and that's what I tried. #msg3010984 Decide for yourself. my review of the DMM6500:
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