Most likely prepare to purchase a new battery. Each time a battery is discharged, it's abilities are severely lessened, about 3 total discharges and it's kaput. Likewise if it's 3-4 yrs. old - that's the avg. life. Others may have batteries older than this, but it's generally the exception.
Each Boxster comes equipped with a manual release cable for both the front and rear hatches. Normally, these are fitted up under the bumper on the pass side. If you're lucky, you'll find it straightaway. If not, you may need to remove the inner fender to locate it. Once you find it, just pull to open the hood. Then take some tape and locate the cable where you feel it's easily accessible (many put it just inside the pop-out for the tow hook.
In the future, if storing the car, it's best to remove the battery and keep it on a maintainer throughout the winter - you'll get more life out of your battery if you do.
