I have a briggs &strattonengine in my ride on lawn mower the battery won't charge when the engine is running

If the battery will not hold a charge: The problem is either a bad battery, or a problem in the charging circuit. First, charge the battery. If it is at all low, it will not start the engine. Clean all connections, corrosion is 80% of all electrical problems. Check that the fuse is not blown. In the wiring harness somewhere there is usually a fuse, look under the dash (If it is a push mower, there may be no fuse), or follow the wires the come out from under the flywheel. There will be a fuse holder & fuse. The battery should read 11-13 volts (push mowers may be 6 volts), check it with a voltmeter and record the reading. Then check the battery voltage with the engine running (if possible) it should be higher, about 13.5 volts (7-8 volts for a push mower) if it is, the charging circuit is functioning. The typical battery lasts 4 years. Most auto parts stores will load-test it for free, but charge it first for an accurate reading.

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