Battery voltage needed to start???

[Steve in Mo 3]

I have a C-101 with the 10 HP Kohler engine. Has always started well until the last month. If it sits for even a couple days it wil not turn over. The battery reads 11.7 volts. I put my jump starter on it and it will turn right over and start. then it will start up all day with no problem. any ideas will be greately appreciated.

As always thanks for the help.

[Save Old Iron 1,573]

Steve,

Read the voltage again as you are trying to start the tractor.

I'm guessing the battery voltage will drop down even lower - probably below 8 - 9 volts DC. If so , the battery has probably developed a high internal resistance and needs to be replaced.

Start the tractor with the jumpers, measure the battery voltage again.

If the charging system is working well, you should see 14 - 15 volts across the battery terminals.

If the battery does not eventually charge to the 13 - 14 volt range, the battery needs to be replaced.

Give us an update.

[pfrederi 19,298]

Fully charged 12 volt should read 12.6 volts. 11.7 is way low and like old iron said when you hit the starter probably goes wayy down. When you have a several battery dependent vehicles you should try to pick up a load tester...they go on sale at Harbor freight periodically for around $25. Or you can drag the battery to the auto parts store as they will usually have a tester....

[Save Old Iron 1,573]

When you have a several battery dependent vehicles you should try to pick up a load tester...

very good advice. at this point in my life with grand-kids circling about, time is just as important as money.

A trip to the auto store to test a battery - possibly to find out it is OK - is an absolute waste of time. The load tester is a great tool to have.

[HankB 16]

Fully charged 12 volt should read 12.6 volts. 11.7 is way low and like old iron said when you hit the starter probably goes wayy down. When you have a several battery dependent vehicles you should try to pick up a load tester...they go on sale at Harbor freight periodically for around $25. Or you can drag the battery to the auto parts store as they will usually have a tester....

Having used Sun battery testers in a previous life, I won't argue their usefulness. However, watching the battery voltage while cranking is a good diagnostic and can be a good approximation of a battery tester.

Here's the next thing I would test.

1) With battery fully charged, crank the engine and check battery voltage (while cranking.) It may be helpful to prevent it from actually starting by shorting the plug wire or simply not pulling the choke on a cold engine. Battery voltage should remain above 8.5V. If it drops below that, high internal resistance should be suspected. Measure at both starter and battery posts to identify possible high resistance in a cable or connection as that can have the same result.

2) If battery voltage is good when fully charged, let the tractor sit several days and repeat the test. If the results are different, then the battery is self discharging or something on the tractor is discharging the battery. You can diagnose this by disconnecting the battery cable while it sits to see if it still discharges. One possible cause of excess self discharge is a dirty battery case that provides a conductive path between battery posts.

Some things to keep in mind...

It is always worth the trouble to disconnect, clean and reconnect battery cable connections. Both ends. If there is a ground strap between engine and frame, do that too. DAHMIKIJK.

Excessive battery voltage drop under load can be caused by incomplete charge or excessive internal resistance. That is why you need to fully charge a battery before load testing it. If you have an incomplete charge after several days, you need to determine why that is happening as it may not be the battery. Replacing the battery if there is some other problem will not solve the problem.

So do these tests and/or load test the battery and let us know what you find.

Good luck!