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Old 05-30-2013, 08:04 AM   #1
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Battery question

A recent motorhome magazine article noted that a fully charged battery (100%) should read 12.7 to 12.8. I checked the coach batteries (2) and got a reading of 12.63. I normally keep it plugged into shore power but it had not been for a few days so this seems OK. The engine battery was 12.76 which I normally keep on a charger but had also not been hooked up for a few days. I then checked the toad's battery which was 12.35. I drove it for a day and got around a 12.4 reading. According to the article this would indicate that the battery is only charging between 50%-75%. The battery is only 2 years old and I always check the water level and add if needed, which it seldom does. I've never had problems starting the car.

Do I have a problem? When we tow I leave the accessory to the on position to unlock the steering wheel. I don't know if the battery is charging while I am towing.

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Old 05-30-2013, 09:05 AM   #2
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Toad battery would only charge if it had an auxiliary source of power to it.

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Old 05-30-2013, 09:29 AM   #3
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Do you have a temperature sensor on the battery? A battery needs a higher charge if its colder out and a lower one if its hotter out. A lot of the charging systems now come with a temperature sensor to put on the battery so that you get the charge you need for the temp it is and the battery you have.
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Old 05-30-2013, 10:29 AM   #4
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Not sure what the article said but here is what most use a reference standard for battery condition (approx 75 deg F average):

This is with engine OFF and after the surface charge has been bleed off (For toad - Lights on for 1 minute).

If the converter, inverter/charger, solar, or engine is running you will be reading the output of the charging device, not the condition of the battery. That table shows a battery at rest (no loads connected, no charge device ON)

A toad voltage of 12.4 (with key ON) after several hours of being pulled behind the coach would be normal if there is no charging connection to the toad from your coach.

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Old 05-30-2013, 04:34 PM   #5
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No, you do not have a problem with the coach batteries. A fully charged flooded cell battery = 12.6 VDC. A fully charged AGM type battery is 12.8 VDC.

I doubt the toad battery is charging. To check, take a toad VDC battery reading before connecting to the coach. Start the coach with the toad connected. Wait a couple of minutes and take a VDC reading on the battery. If it is the same as the first reading the battery is not being charged. If the reading is higher than the first reading, the battery is being charged.
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Old 05-30-2013, 05:20 PM   #6
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As pointed out, I doubt you have a problem with any of your batteries... but, are you taking the readings directly from the battery post or through the battery cable clamps? Corrosion on those mating surfaces can cause voltage drop.

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Old 05-30-2013, 06:09 PM   #7
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Thanks to all. Think I will be installing the 'Toad-Charge'. Doesn't look like a big job.
Rick, readings are taken from the posts.

Thanks again.

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