After charging my battery yesterday, when I came to go for a ride today the lcd display said the battery was half empty. When plugging the charger in again, it went straight to green. Checking the battery with a voltmeter it reads 36.9v so I guess the display was correct. What should I check next? Battery and charger are both only 6 weeks or so old and have been ok until now. Probably used about 10 times.