Possibly your alternator not working properly and not charging your battery up like it should. That's what it was on my Clio (although I wrote it off before I got a chance to swap the alternator and find out if that cured it).
Tested my battery it should be 600en but only had 451 weird thing was day before it had a long run whats best way to test the alternator
It did drop to 14.7 to 14.9 with no head light since iv swapped the battery we retested the old one and the charge had gone up to 570 en
