What is the relevance of "Low Signal" in battery usage stats?
You’ll see “low signal” when you are using service in a poor reception area. When the phone needs to search for a signal all the time it uses more battery life. We normally see this on Home &amp; Lock Screen and Personal Hotspot. The best thing to do to save battery in these situations is look for a way to get a better signal, or maybe even turn cellular off when you are in really bad reception areas. You can turn off cellular by going to Settings -> Cellular -> Off. With this off you can’t make calls, so you don’t want to leave this off all the time, but it can help in some situations.

"Better" is relative so the percentages would probably vary by situation.