For every start of your car you need to drive at least 15-20 minutes in order to recover the energy your battery lost during engine start and it’s even longer if outside temperature is very low, -15 deg Celsius. If you drive a short distances and start frequently your engine, your battery will loose its capacity and sometime will not be able to start you engine. This charger is a perfect solution for keeping your battery in a perfect shape, specially during winter months. I connect it to my wife’s car once a month in order to keep the battery almost fully charged. I use its Slow mode function in this case. I encourage every one driving frequent and short distances to buy this very inexpensive and technically great charger.