Wife came home Sunday afternoon and unloaded car. This morning (Tuesday) she can't find her keys, I give her my set. She goes out to the car and comes back in. Says her keys are in the ignition (!) but the car won't start. She takes my van. I check and nothing powers up. Check battery with voltmeter, get 3.1 volts. I don't know if she left the ignition on or had it in Accessory position or what. Hook up portable battery(has led that says it is at 85%), won't start but cell phone charger indicator lights up. Hook up charger, not expecting it to hold a charge. After a couple of hours I can start it. Charged it the rest of the day. Tomorrow I will take it to AutoZone and have them test it. Any opinions about whether I can trust this battery if it still holds charge tomorrow? It is original battery and is over 3 yrs old and car has about 31,000 miles on it.