Batteries come in a large variety of models and sizes, with chargers being just as varied to match. No matter what the individual model or complexity of the charger, however, reading the battery charger gauge is essentially the same. The reason behind this standardisation of the gauge information is to promote general use among consumers. For you though, it means that whatever the charger necessary, you'll be able to tell at a glance how charged the battery is, and how much remains before the battery reaches storage capacity.
Connect the battery charger to the battery you intend to charge without plugging the charger in. Hook the positive clamp of the charger, the red one, onto the positive terminal on the battery. Hook the negative clamp, the black one, onto the negative terminal. Secure the clamps firmly by testing them for slippage or wiggle on the terminal. Adjust the connection as needed.
Input the settings options into the charger. The extensiveness of the settings will vary by charger model. Common settings include amp settings, voltage settings or battery type. Select the setting that matches your specific battery.
Plug the battery charger into an electrical socket. Turn on the charger and set the charger timer. The timer limits the length of the charge, cutting power to the charger when time runs out. Time settings depend on both the model of battery as well as the model of the charger. Consult the manufacturer's user manual to determine timer-setting lengths. Automatic chargers will not have timers, as they shut down upon detection that the battery is fully charge.
Examine the gauge to determine the charge state of the battery. Check the location of the gauge pointer in analogue gauges. For an AMP gauge, the pointer shows the charge going from the charger to the battery. The pointer begins in the red area, indicating a high initial charge rate. As the battery gains a charge, the rate will diminish, moving toward the green section of the readout. When it reads 1 or 2 amps then your battery is near full capacity and you can stop charging.