I OWN A 1977 172XP THAT I PURCHASED IN 1992. COMPLETELY REFURBISHED WITH FACTORY NEW IO-360KB ENGINE, WINDOWS, FAIRINGS, PAINT, ETC., ETC. I HAVE HAD AN ON-GOING PROBLEM STARTING THE ENGINE DURING PROTRACTED PERIODS OF DOWN TIME, PARTICULARLY DURING THE COLD(ER) WINTER MONTHS. THE 12-VOLT GILL BATTERY (NEW OR OLD) DOES NOT HOLD A FULL CHARGE.  I HAVE TAKEN THE BATTERY HOME, BROUGHT IT UP TO FULL CHARGE AND, AFTER TWO DAYS DISCONNECTED FROM THE CHARGER, IT DROPS DOWN TO 65% CHARGE, NOT ENOUGH TO START THE ENGINE. AT FULL CHARGE OR USING JUMPER CABLES TO MY CAR, THE ENGINE STARTS EASILY.  THE PROBLEM IS THE 12-VOLT SYSTEM, THE BATTERY INSTALLED IN THE REAR OF THE XP AND THE VOLTAGE DROP TO THE ENGINE STARTER. I WANT TO INSTALL A POWER PLUG IN THE BAGGAGE COMPARTMENT TO MAKE IT EASIER TO CONNECT A PORTABLE POWER UNIT OR MODIFIED JUMPER CABLES TO MY CAR, ELIMINATE THE DISASSEMBLY REQUIRED TO GET AT THE BATTERY.  ANYONE????????