Hi guys, i've recently replaced my 2.9 vr6 engine out f my corrado with a 2.8 stage 2 supercharged lump. I replaced the battery at the same time and its lasted some time but recently as i've ben driving back and forth the garages its started to lose charge it seemed to completely run out and when i started it after charging it for 15 minutes it didnt seem to last anymore than 5 minutes it would cut out as the car was going? The garage put a voltmeter across the battery to show it losing charge i just wondered how i test the alternator or any common problems that occur? I do have a spare altern