Like JRH said, long term storage (over 2 weeks I would say) without use should be done at half charge. Even Maxamps specifies this. And doing so might make any possible warranty claims easier on you. For shorter terms, keeping at full charge is OK.
To charge halfway, just run your vehicle until the LVC kicks in and then charge until about 1/2 the mAh rating is put back in.
Or, depending on the capabilities of your charger; set your CV/CC threshold to 3.7v/cell or 3.8v/cell and charge normally. The lower setting will put about half charge in.
Or, if you already have a fully charged pack, discharge it using the charger (if capable) until 1/2 the mAh rating is taken out. But, it's more fun to use the battery in a vehicle than sitting there watching it discharge.
Not to mention a wasted discharge cycle out of its life.