The BatteryMINDer® Battery and Alternator Condition Tester (BACT) tells you the condition of both, with a simple press of a button. The unit's multicolored LED indicators accurately respond to the battery's voltage. The user simply needs to press the test button to know the condition of his battery. With the engine on, a press of the test button indicates whether the alternator is putting out enough to properly charge your battery. Model 12104 works with all size and type 12 Volt batteries. It is waterproof and small enough to fit on the top or side of even the smallest battery. The unit draws no power until the test button is pressed. Two (2) wire connections to the post screws or clamps of the battery and attaching it with the supplied marine grade Velcro, completes the installation.