Try driving with the sidelights turned on for your trips, the alternator will charge the battery at 14.4 Volts for most of the journey, when driving with the lights off, the battery is charged intermittently, note only;y the sidelights on, the swit6ch in the middle position, not with the headlights on. alsdo go on ebay and buy a usb charger with a voltmeter to plug into the power socket, so you can keep an eye on the charging system