I purchased the DBPower about a month ago. I went away on vacation for a week and when I returned my car batter was dead. A great opportunity to try the DBPower. Conditions were as follows: Engine is a gas 6.0L, Battery was drained enough that interior lights would not even come on. It was 26 degrees F at time of trying to start and the DBPower was at 99% charged.
I connected the unit as per instructions. It provided enough juice to get the lights to come on and engage my alarm but did not start the car. I contacted support and they are in the process of sending a replacement to rule out the possibility of a bad unit. Great customer support thus far.