Sounds like your batteries were dying and you didn't know.
This is actually another aspect of meter safety. Ideally, the meter will stop allowing you to take readings before a low battery would result in a bad reading.
So, from a safety POV, the best case is if the meter detects a low battery it indicates low battery and locks out the display until the meter is turned off. The Fluke 113-117 meters do this. If your battery is marginal sometimes turning on the backlight will trigger the low battery display.
I think some meters will turn on a low battery indicator but allow you to still take readings until the display fades out. This is fine so long as those readings are within spec.
Not so good is when the battery indicator turns on but the meter can still take reading but now they may not be accurate. The free HF meters behave like this.
Worse case is the meter shows no battery level warning. Instead it just stops meeting it's specifications.
This low battery issue seemed to be a bigger problem with older digital meters. The newer electronics, even on cheap meters, seem smarter about low battery conditions.
OP, I would suggest watching some of Dave Jones's (EEV Blog) videos about multimeters. They are educational with regards to what to look for in a good meter. Some of the meters are likely still available but I suspect most have been updated since his videos first went out. Still, it's a good education.
