Trickle chargers are great, but sometimes at low amperage, they dont fully charge your battery, especially if the battery is weak to begin with. For this reason, we strongly recommend also that you have a higher power charger available so that you can both use a more powerful charging system and also start your car if the trickle charger doesnt keep it up to snuff. I get many phone calls from folks telling me that the trickle charger has been on for a long time and the car still wont start and its often because theres only so much a trickle charger can do. Its great for maintenance, but if your battery is really low or somewhat weak, all it will do is maintain that weak condition. Therefore, its smart to have a higher amperage charger available for those special occasions when your battery is just not up to the task.
We use these in our shop all the time to make sure the batteries in our building are really fully charged.