Check the battery with a voltmeter. An hour and a half of riding could deplete the battery depending on how much assist you are using. If it reads somewhere around 40 volts it's depleted. Inability to hold charge is a sign of a battery that is cooked. Fully charged a 48 colt battery should read about 54 volts. You may have the option in your display to monitor voltage rather than percent capacity remaining. The latter can be inaccurate.