So I have a 2007 XC90 V-8 sport. It is acting like the battery/alternator aren’t working properly—not having enough juice when I try to crank it. I’m sitting in the AutoZone parking lot, having just had my battery and my alternator tested. Battery is full/alternator is working properly. Car still acts like the battery is dead and will not crank without a jump. When I attach a jumpstart power pack, or jumper cables from another car, it starts right up, so I assume the starter is OK. I am lost on this. Any ideas?

 

did you inspect the battery cable and ground strap as well as the cable from the battery to the starter for any signs of bubbling insulation and corrosion?

How old is the battery? Is it reading 12.6V? where does the voltage go when you hit start? If you can't start the car without a jump, the alternator's not in play so it is either the battery, the cables or perhaps the starter motor. The alternator could be under-charging killing the battery, so once you get it jump started check your voltage again at your battery terminals with the engine running at idle - should be 14V+. Now throw on an electric load (rear defogger, high beams, blower on high, stereo blasting AC/DC...) - Voltage should stay over 13.5V, certainly more than 13...

Next after that is to clean and tighten the battery terminals and cable terminations. If your starter cable has bubbles, is hard and feels lumpy, time to replace. If the voltages are not to spec, it may be the voltage regulator or alternator - on some models the regulator can be replaced separately but on the cars with the load sensing circuit, they are very sensitive to having the exact correct alternator part (enough people on the board have noted replacement alternators not working quite right and wound up dropping in a genuine Volvo part or a worked used one...)