Car seems to be charging ok but some thing

Check for consumers staying on such as interior lights , radio etc.. To check for current draw, you need an AMP meter. remove the negative battery terminal. Connect one amp meter lead to the battery negative terminal and the other to the earth cable. Hold the cable against the battery negative cable, close all doors and press bonnet switch to closed position. Activate the alarm and wait for it to arm. Once it has armed itself, separate the earth cable from the battery terminal keeping the amp meter connected. read the current draw. Should be less then 100 milli amps. Usually +- 40ma. To check which circuit has current draw remove one fuse at a time and check if current draw drops. A drop in current draw will indicate that the problem is on that fuses circuit. Also check alternator charge rate. To check this hold a volt meter across the battery terminals. with engine off, should get battery voltage. Start the vehicle, battery voltage should rise to 13 -14v and maintain this voltage with the headlights on. The battery itself could be faulty, you would need to do a load test on the battery. Load tester needed to do this.

Does it have a trunk light? look though back seat?