Recently took friends car to local parts house to test battery. Because of a medical condition, her car sits, sometimes for as much as a month or more. I had just charged battery using Battery Minder. Parts house told us alternator wasn't working, and she needed a new one. Took it to where she buys tires, and they also checked it. Said everything GOOD! Always get a SECOND OPINION! FYI, Northern has Battery Minders on sale right now for about $30. I keep one on the battery in my stand by generator. Battery was made in 09, which means it's thirteen years old. Cranked generator in monthly test earlier this week with no problems. Once a month, run Battery Minder on each vehicle for at least 24 - 48 hours. Cheap insurance IMHO. Before shelling out $140 for a battery, check out Walmart's $54.99, "one year free replacement" battery. We have three vehicles running them. Oldest is on it's third year of service.