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Starting Battery Confusion

Hello all,

I'm back to messing with the starting batteries again.  Many years ago I replaced a single 4d battery the coach came with with 3 optima red top 35's.  These 3 batteries were only able to start the coach without boost for a short time.  Now the coach struggles to start with boost and my boost solenoid stopped working.  I got a new solenoid but Ithought I would dig in and investigate.  I thought I had a connection problem but I can see the battery voltage dropping to 6v when attempting to start so the cables are good, the batteries aren't good enough anymore. 

I am scratching my head a bit as to why I would have bought 35's when everyone seems to have group 31 or 34.  I measured the tray and it is just over 9 3/4 wide by 21 long.  I really don't understand this.  Did foretravel really build my tray to only hold a single 4d battery?  Not even 6d or 8d?  What am I missing here.    This is a 1999 U320 42'.  The 35 batteries are pretty small looking. 

Re: Starting Battery Confusion

Reply #1 –
Quote from: Mark D –
  Did foretravel really build my tray to only hold a single 4d battery?

Your coach should have came from the factory with 3 Optima batteries. Some were the red top and some were the yellow top no rime or reason as to which they used.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Starting Battery Confusion

Reply #2 –
To add to Mike's reply, start battery tray while it holds 3 batteries, factory only put in 2 Optimas for U270 with 8,3 engine.

Many added a 3rd Optima to spin C8.3 engine better.  An easy inexpensive mod to help engine starts.  Of course this mod is better made when replacing the two batteries, so all three contribute more equally. 

 

Re: Starting Battery Confusion

Reply #3 –
But according to my measurements the common batteries people seem to use (group 31 or 34) don't seem like they'd fit.  I put the 3 35's in but I never really like how they worked.  Maybe I have wiring issues on top of the batteries.. 

Re: Starting Battery Confusion

Reply #4 –
There are a host of issue related to starter and cabling...(just tore mine apart and redid). 

First is the type of lugs used on the cables.  At first the serrated faces of the lug may seem like a good idea, but only of value on a soft mating surface...like a battery terminal.  The serrated faces reduce surface area and allow for corrosion to form between the surfaces. 

FT had this habit of stacking too many lugs and depending upon how they are stacked, the lugs make for higher resistance, especially under starter loads. 

Proper Battery practices were not followed for parallel batteries.  Should be Positive connected to one end of the parallel string and negative to the opposite end...makes for better balanced charging, discharging and battery health.

Back to the terminal lugs and battery jumpers.  The terminals all need to be cleaned and treated with anti-corrosion compound.  That is all the way from the batteries to the studs, to the starter and ground connections. 

I replaced the battery jumpers with 4/0 and flat faced copper lugs.  A fine point to consider is the way the lugs are stacked on the batteries.  The Pos and Neg going to the studs should be the first on the appropriate battery terminal with the jumpers on top.  Makes for more even and efficient power transfer from the batteries to the chassis/started feeder cables.

Nut/caps on the battery studs should have a copper or stainless washers to help provide even compression of the lug stacks....all connections should have anti-corrosion conductive paste (used very sparingly) on every connection face.

For me, I was already committed to replacing the starter with a gear reduction unit, BUT I did all the battery prep (new jumpers, cleaned and treated all connection and tested batts to ensues good....and guess what, old starter spun the engine up as if it had boost on...and voltage drop was substantially lower during start. 

My chassis batteries are standard Gp 31 East Penn 975 CCA wet lead acid, nothing special.  I will note I have added a IOTA 15 amp, 4 stage charter that maintains the batteries when plugged in or on gen.  It's designed to do an equalize/desulphation anytime the coach has moved not in seven days.  Also my newly installed Sterling DC-DC can do a reverse charge of 20 amps off the new house lithiums....

Moral of the story is good connections, proper lugs, properly sized wire, logical battery wiring and healthy batteries will crank with no effort....and yes, an ISM here. 

I did complete the starter upgrade to a Delco-Remy gear reduction unit and love it.  Very little voltage drop, lower current surge and a solid crank....about twice as long, but that's ok...

Questions, feel free to PM....

Bob

2002 U320
3620 PBDS
Build 5985
2021 Equinox Toad
Motorcade 19006 & all those "other" clubs too!

Re: Starting Battery Confusion

Reply #5 –
Quote from: Pamela & Mike –
Your coach should have came from the factory with 3 Optima batteries. Some were the red top and some were the yellow top no rime or reason as to which they used.

And ours for '03 were 3 Optima blue tops, group D31M.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Starting Battery Confusion

Reply #6 –
I just redid the wires and the lugs on my 2003 U320, the starter was dragging pretty bad and the boost helped  I also added on off switch for the start batteries case I need it down the road. My batteries now have their own dedicated wire up to the new buss bars the old single lid bolted to the frame is gone and  I had to replace the wire from the new buss bar to the starter because I found that from the factory the wire that goes to the starter was rubbing on the air hose for the tag brake can. So now I have replaced wires from battery's to the buss bars, new buss bars, on off switch, a new 4/0  wire that goes over to the new gear starter. It starts like it's brand new without the boost switch on.
The selected media item is not currently available.Keith & Jo
2003 U320T 4025 PBBS Designer series
Build 6203    Cummins 500hp
2000 U320 4010 WTFE / Build 5762 —Sold—
Motorcade #18070   
Pasadena, Texas
2015 Jeep Wrangler Sahara-Sunset Orange pearl coat
Don't argue with a fool, people watching might not be able to tell the difference.

Re: Starting Battery Confusion

Reply #7 –
Had 3 Optima yellow top Group 31's in my coach.  When they started dragging, I replaced with 3 Duracell Group 31 batteries.  They fit the tray in my '03 U320.

Keith
2003 U320 38' #6197

Re: Starting Battery Confusion

Reply #8 –
Your tray looks identical to mine and yet I only have 9 3/4" width available.  Hmmm..  The internet says the group 31 batteries are 13" wide.  I've also noticed that the wiring near my starter feels... crispy.  Probably going to order some 4/0, a crimper and flat terminals.

Re: Starting Battery Confusion

Reply #9 –
When I replaced my starting batteries I was told Cummins wanted 2100 amps for starting an M11.
So I guess any size / number of batteries that will provide 2100 amps of cranking power should give good cranking speed.
John Duld
1995 U320C SE 40'

Re: Starting Battery Confusion

Reply #10 –
I have 4 optima red tops on my 2000 u320
Michael Carty
 

Re: Starting Battery Confusion

Reply #11 –
I put in new interstate MTP-35's from costco.  Good price.  It can now start again without boost but spins a good deal faster with boost.  I notice now that the battery interconnect cables I made back in the day are only 2/0.  Between that and the crunchy positive cable to the starter I think I will order some 4/0, terminals, bus bars, and one of those fancy hydraulic crimpers.  Should be able to make it work well.