Briggs and Stratton engines equipped with batteries and alternator charging systems can typically be found on riding mowers, generators and pumps. Although classified as small engines, their operation and system component functions can be likened to miniature automobile engines that have fewer cylinders and have more compact designs. The charging system for the Briggs and Stratton engine begins with the battery, which supplies voltage to the starter. Once the engine runs, the alternator takes over the electrical delivery, supplying voltage to the spark plug and sending extra current to the battery for recharging.
Remove the cover cases to allow access to the battery and alternator. Many riding tractor batteries can be located under the driver's seat, while the alternator must be accessed through an engine side or top cowl. Apply the emergency brake on the vehicle and place the transmission selector in "Neutral" or "Park." Disengage power to the cutting deck. Turn the ignition key to the "Off" position. Use a screwdriver to check the electrolyte level in the battery cell, by unscrewing or popping the battery cover caps off.
Fill each battery cell up to the inside neck of the battery with distilled water. Disconnect the negative battery cable with a socket, then the positive cable. Clean the inside of the cable clamps with the wire end of a battery cleaning tool. Use the female wire end to clean both battery terminals. Reconnect the battery cables with a socket.
Place the red (positive) lead of a multimeter to the positive battery terminal and connect the black (negative) lead of the multimeter to the negative battery terminal. Switch the gauge to volts.
Look at the volt reading on the multimeter. It should register at least 12.5 volts. If not, slow-charge the battery and take another reading. If the volts show significantly less after the charge, the battery has a defective cell and the battery should be replaced. A 12-volt battery that has a dead cell will read two volts short of its maximum charge.
Start the engine and let it warm up to normal operating temperature. Let it idle with the choke off. Hold the red lead of the multimeter to the positive terminal of the battery. Place the black lead of the multimeter to the negative terminal on the battery. Look at the charging voltage. It should read approximately between 13.2 volts and 14.6 volts, or according to your charging specifications in your manual. Any reading less indicates a problem with the rectifier, alternator, or regulator, if so equipped.
Refer to your owner's manual for the location of the rectifier. It appears as a small metal box and will have a number of spade wires connected to it. Some wires route from the ignition switch, whiles others go to the alternator. Set the multimeter for ohms resistance and beep tone. With the engine off, touch the black probe of the multimeter to the outside case of the rectifier. Touch the red probe of the multimeter to the spade terminals on the rectifier marked, A, B, C and D.
Look at the gauge. The screen should display "OL" after touching each terminal. If the screen fails to show an "OL" indicator, or beeps during any touch of any terminal, it indicates the rectifier has a direct short to ground. The rectifier must be replaced.