What app are you using? I haven't used the 3DR app in ages, but I know Solex should be able to tell you how much battery you have remaining. If solex is showing the info but your controller isn't, could be a setting or a controller issue. If neither is showing the info, it could indicate a battery issue.
Did you or someone else open the Solo? Open it back up and look at the area around where the battery contacts go. Is there metal shielding(for GPS) around there? If so trim it back and put the Solo back together.