If I understand your question right, you need to use filldown
UPS_BATT | timechart max(UPS_BATT) as UPS_BATT span=1m | filldown UPS_BATT
Documentation here - https://docs.splunk.com/Documentation/Splunk/8.0.0/SearchReference/Filldown
Hope this helps
If the problem is that you're seeing the graph go to zero between readings on a line chart, under Format, you'll find a setting for Null Values. Set that to "Connect" and you should see those gaps go away.
If I've misunderstood your issue, please expand your explanation. Screenshots for this sort of thing are helpful, too.