sorry i forgot to give the modle number oh and by the way i had to get the modle number off the motor not off the motor becaues someone before me had changed engine before.here the modle 13df675g062 serial number 1j42h10602

If the motor has been replaced with a different model, its possible that the new motor has more power, which draws more current, and drains the battery in less time. In other words, its possible that everything is working just fine, with no repair required. Can you speak with the person who modified the mower?

no i dont think that it.the motor on it before was 18hp and this motor is a 14.5 briggs.this problem just started less than 3 days ago.what do i need check on the charging system?

Sorry, I misunderstood your situation. The alternator on your mower might not be working. I would look for loose wires, a connection that is not tight. The first thing to do is inspect the wiring to the ignition switch, alternator, and the battery.

I went to the MTD website, where you can get an Owner's Manual, Parts Manual, and Briggs IPL, all for free.

According to that info, you have a conventional split alternator, which has an AC output for the lights, and a DC output for charging the battery. There are two wires from the engine coming to a connector. The connector then goes to the tractor's wiring harness. The DC wire has a diode rectifier (it's a hump in the wire under heat-shrink tubing) which stops electrical flow in one direction, converting AC to DC.

Do you headlights work? If so, the alternator is probably OK and the diode may be bad. If the diode is open (no flow either direction), it won't charge battery, but you shoould last for a couple of mowings. If diode is shorted, it will pump AC into the battery, and will probably ruin it in a few running hours.

The electrical system does not have any load on the DC side, other than to charge the battery, and of course to power the starter motor. The lights pull power from the AC side, and also don't draw power from the battery.

If the diode proves to be bad, and you're handy with a soldering iron, you can replace yourself. If the alternator coil is bad, it gets more complicated and expensive. You have to remove the flywheel, and the remove the alternator coil, and then put everything back together. BTW, I'm not talking about the ignition coil. It is completely separate and has nothing to do with the alternator.

Here is a link that might be useful: MTD Manuals