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Old 04-22-2018, 03:55 AM   #11
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Hello Burlking,

I'm guessing that you're thinking a two battery setup too? IU found some defect pricing on 2 size 31 batteries for less that $100 each. The guy told me they are a very popular size.

Your thoughts?

-Lewis
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Old 04-22-2018, 08:07 AM   #12
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Group 31's are $79 brand new at Rural King.
I've been using them for years.
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Old 04-22-2018, 12:18 PM   #13
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It all sort of depends upon where the battery(s) were located.

If under the hood, most likely a single group 31 battery.

If in a battery compartment located in the skirt of the body along the frame rail it could have had one large 8D, or two/three Group 31 batteries, or two 8D batteries. I have seen some skirt mounted battery boxes that were just that, boxes. In that case changing the size of the battery or number of batteries is not a big deal. Others I have seen have had racks that will only fit a certain size battery. Regardless, choose whichever will fit the best.

For your purposes you don't need much more battery than one high capacity Group 31 or one 8D battery. Most buses have multiple batteries for the reserve capacity. When you have six or more heaters, defrosters, and blowers in addition to crossover lights, interior lights, running lights, headlights, and roof strobe lights it takes a lot of juice to keep them all going. Even with 150+ amp alternators it is hard to generate enough juice at idle to not use more than what is being generated. Since you will be doing very little idling with much more than a few lights you won't need the reserve capacity for that and one battery should be more than enough to get your engine started.

Whichever battery(s) your bus had, make sure you use large enough battery cables to reduce the resistance from the battery(s) to the starter. That starter is going to draw a LOT of amps whenever it is turning.

Also, don't purchase battery(s) strictly on price. When you shop around make sure you are comparing apples to apples. I have seen some Group 31 batteries that have had more cold cranking amps and reserve capacity than some 8D batteries.
When buses have multiple batteries do they go in the same compartment and are they wired together somehow so the alternator charges them both?
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Old 04-22-2018, 12:38 PM   #14
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When buses have multiple batteries do they go in the same compartment and are they wired together somehow so the alternator charges them both?
Yes. They are wired in parallel to make one big 12V battery that is charged by the alternator in the normal manner.

Some might have another battery to drive a wheelchair lift. That will be somewhere close to the lift.
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Old 04-22-2018, 05:57 PM   #15
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Yes. They are wired in parallel to make one big 12V battery that is charged by the alternator in the normal manner.

Some might have another battery to drive a wheelchair lift. That will be somewhere close to the lift.
Twigg hit the nail on the head, but if your not familiar, parallel is + to + and - to -. That makes the two batteries appear to be one big 12v battery to the bus. I think there were a few buses that were 24V, which in that case they would be + to - between the two batteries (series), but I don't believe 24V was very common in buses (except maybe the military).
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Old 04-23-2018, 11:19 AM   #16
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Twigg hit the nail on the head, but if your not familiar, parallel is + to + and - to -. That makes the two batteries appear to be one big 12v battery to the bus. I think there were a few buses that were 24V, which in that case they would be + to - between the two batteries (series), but I don't believe 24V was very common in buses (except maybe the military).
Well I learned something new today! Assuming my battery compartment pullout can handle the weight (and I have no idea how to verify that) is there a down side to chucking another battery in there? Seems like good insurance against it not starting and or being able to run something on that power for pretty cheap.
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Old 04-23-2018, 11:36 AM   #17
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Well I learned something new today! Assuming my battery compartment pullout can handle the weight (and I have no idea how to verify that) is there a down side to chucking another battery in there? Seems like good insurance against it not starting and or being able to run something on that power for pretty cheap.
Don't just add a battery to one of unknown age and condition.

When you are ready to replace the battery you have, buy two and do it then.
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Old 04-23-2018, 02:55 PM   #18
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Yes, I believe they were in parallel. I've got to hook up all the wiring to the bus as well as they just went on a cutting rampage and just cut everything to get the batteries. I'm going to put 4/0 wires so it will all match what goes to the starter.

Lewis.
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