I've had my 2012 Prius C for about a month now (1100 miles) and am happy with it -- but today, for the first time (I believe), I noticed the hybrid battery meter was showing only 6 bars rather than the usual 7 (I've never seen all 8 illuminated). Then, during the day, it fluctuated down as low as 3 bars -- then back up. Is this normal? Does this mean the batter is in trouble? Thanks in advance for any info!