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Old 03-10-2019, 11:40 AM   #11
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I think the draw is minimal, just memory, don't forget your stereo has a memory drawing constantly. The best choice is to disconnect a battery post or trickle charger. I have a truck sitting and use a solar charger to keep the batteries up. A lead acid battery discharges from 6-20% a month depending on weather from what I just read.
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Old 03-10-2019, 11:55 AM   #12
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From the sounds of it, you replaced one battery without having the others tested. One weak battery will discharge others in a system (assuming they are not isolated) and eventually kill them.


Quote:
Questions:
I have three Group 31 batteries. Is that optimum?
Should I pull each battery and test individually?
Are my batteries toast and need replacement?

1. Should be fine, unless you have a really big engine to start. A C7 engine should be fine with just two, some states or school districts require a minimum CCA rating from a battery (or multiple batteries) or a certain reserve. Many engines will start fine on just one good strong battery, though it will spread the load across more batteries and help them last longer.
2. YES! Every time.
3. Without testing, I'm only guessing, but it sure sounds like it.


I can buy Group 31's locally from an independent battery shop for about $70 each - my bus has 2, but the battery bay can hold 3 (and eventually might). Road tractors and many commercial trucks hold 4.
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Old 03-10-2019, 11:59 AM   #13
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Originally Posted by sportyrick View Post
I think the draw is minimal, just memory, don't forget your stereo has a memory drawing constantly. The best choice is to disconnect a battery post or trickle charger. I have a truck sitting and use a solar charger to keep the batteries up. A lead acid battery discharges from 6-20% a month depending on weather from what I just read.

My bus does not (yet) have a radio, the ECM draw (if any) is so low it is practically negligible. I should get a solar trickle charger, but many plug into a cigarette lighter (which my bus also lacks). I'll either have to add one, or find a hard wired version.
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Old 03-10-2019, 12:11 PM   #14
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Originally Posted by TeacherJoe View Post
Thanks. Thatís what I was thinking. However, I donít want to throw batteries at a faulty system. I feel like I need to rule out a parasitic draw. Am I overthinking it?

Joe
No, you definitely want to fix the issue before destroying your new batteries.My 37' Genesis only uses one battery, no issues starting it. Might start with just one till it's figured out.
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Old 03-10-2019, 01:20 PM   #15
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FYI, my bus's DDEC engine computer draws 8mA when the engine's not running.

I use two Group 31 start batteries (with the DDEC powered by battery 1), and each of them is connected to its own Ultra Trik-L-Start battery maintainer that keeps them always fully charged. As long as I have two green lights showing I know I'm always ready to start.

John
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Old 03-10-2019, 03:05 PM   #16
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Inceni john.
I was just looking at a motor upgrade with the DDEC and EMC for my all mechanical bus?
Do they require constant power for memory retainage?
For the teacher Jo.
On any 12v system every thing is almost grounded buy the mounting plate of the fixture and screw into the body metal. Any of the body/chassis grounds whether main body to chassis or old light switches that don't quite turn off all the way.
I need to do this myself but I know it is my battery to chassis connection.
Two group 31's should be adequate for our purpose.
If they don't do it then turn the motor over with a ratchet and socket?
Maybe it's topped out on compression stroke at last umph of your old battery.
Should always replace all batteries at the same time.
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Old 03-10-2019, 03:21 PM   #17
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How much draw is there Rick from these computers anyway?
Enough to kill two Group 31's?
Most vehicles get driven and so charge batteries up again but buses do sit more, private ones anyway. I could see it over a few weeks or months happening without charging at all. Something else going on here I presume.


John
My DT466e would drain the batteries after a few months.
I'm sure the c7 is the same.
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Old 03-10-2019, 03:29 PM   #18
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Lots of advice here. My Thomas with a 3126 probably is quite similar electrically. I have LED lights and relays that are active on the four 12 volt load centers that the bus has, regardless of key position.

The only way those turn off is if I kill the main breakers. It can sit for a while with no problem, but a month or more and it starts starting hard.

How long was your bus sitting? How deep was the discharge? Fully draining them is not great for them, especially in cold weather, but it does not automatically mean they are toast.

Even Walmart will test batteries for you, so it is easy to do. Also, as others have said, a good trickle charger can do a lot to bring a borderline battery back to health (assuming it has enough electrolyte).
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Old 03-10-2019, 03:38 PM   #19
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Lots of advice here. My Thomas with a 3126 probably is quite similar electrically. I have LED lights and relays that are active on the four 12 volt load centers that the bus has, regardless of key position.

The only way those turn off is if I kill the main breakers. It can sit for a while with no problem, but a month or more and it starts starting hard.

How long was your bus sitting? How deep was the discharge? Fully draining them is not great for them, especially in cold weather, but it does not automatically mean they are toast.

Even Walmart will test batteries for you, so it is easy to do. Also, as others have said, a good trickle charger can do a lot to bring a borderline battery back to health (assuming it has enough electrolyte).
The bus sat for only a couple weeks. I recently replaced one of the three batteries and the bus started right up. Just yesterday they read 8 volts with a multimeter. I have good advice here and will pull the batteries and determine if they can recover. Unfortunately I canít run a trickle charger where I store it. No electricity. I need to actually figure out whatís going on. Itís all good. This is exactly what I need to learn so I can be competent down the road.

Joe
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Old 03-10-2019, 03:43 PM   #20
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Quote:
Originally Posted by TeacherJoe View Post
The bus sat for only a couple weeks. I recently replaced one of the three batteries and the bus started right up. Just yesterday they read 8 volts with a multimeter. I have good advice here and will pull the batteries and determine if they can recover. Unfortunately I canít run a trickle charger where I store it. No electricity. I need to actually figure out whatís going on. Itís all good. This is exactly what I need to learn so I can be competent down the road.

Joe
You're going to want a disconnect switch if you're going to have it sitting a lot with no trickle charger.
Any time you replace one battery you're typically going to need to replace all three. I've gotten away with it before but usually they go bad quickly unless they're all 100% the same.
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