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Coach Battery Staying Power

When we bought our Foretravel five years ago, we soon bought three new O'Reilly 8d AGM batteries. We have not had a problem with them until our last trip. When we stopped for the night (boondocking), the coach batteries would start losing voltage. It got so low by late night that I turned on the generator to recharge so they would not be a problem to start the next morning. (We have a trickle charger that charges the coach batteries when they are significantly lower than the chassis batteries (three red tops less than three years old)).
 
Since this is our first, and only RV, I do not have any personal experience from which to draw meaningful conclusions about what could be happening.
    When we are plugged in at home or a campground, both sets of batteries are maintained at a full charge.
    When the generator is running, both sets of batteries are maintained at a full charge.
    When the engine is running, both sets of batteries are maintained at a full charge.
    When we are not plugged in, and neither the engine or generator is running, my recollection is that both of the battery banks discharge faster than I expected.
 
Before throwing a lot of coach bucks at six new batteries, what else could be causing these symptoms?
 
Thanks for any hints, thoughts, or observations from this knowledgeable group,
 
Trent

Trent and Jean Eyler
2000  U295  4003  WTFE  ISC  350
Build#5603 MC#17385

Re: Coach Battery Staying Power

Reply #1 –
Boost solenoid stuck in the on position causing both sets of batteries to discharge faster than normal. Have to think a while for other reasons both sets would discharge. You might use a battery tester on all the batteries to possibly find a faulty one. Cheap at HF.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Coach Battery Staying Power

Reply #2 –
Trent,

RedTops are great start batteries but they are not very good at the long tern drain of all the parasitic stuff like a YellowTop or other deep discharge battery would be.  Keep them charged up.

Your 8D AGMs probably started at 225 amp hrs each or more. Over time that capacity will decrease especially if the batteries are not brought back up to a 100% state of charge. 

You can do a load test by fully charging each individually to a 100 SOC and then using an appropriate load tester to determine how they hold charge under load.  With a battery load tester, apply a load equal to one-half of the CCA rating of the battery for 15 seconds.  Voltage will drop.  If it does not drop below the recommended voltage (around 9.5 volts depending on temperature) it passes.

You can do a capacity test to determine what capacity they really have.  You will have to look up a specific procedure but it involved putting on a known load on s fully charged battery until the voltage gets to somewhere around 10.3.  this gives you an idea of how long your battery will last with a given load.

Batteries have a life expectancy usually in cycles.  Discharging from 100% to 50% and back to 100% is one cycle.  50% is about 12.2 volts. Most 8D AGM are in the 1500 to 1800 cycles.  Discharging below 50% reduces the cycle count.  Not recharging to 100% reduces the cycle count.  Limiting the depth of discharge to 75% (using 25% of your capacity) will almost double your cycle count.

It is possible to have a bad cell in one of your 8Ds.  This will screw up your duration.

If your batteries are still OK just aging and you have 200 amphrs in each then 50% of 600 amphrs is 300 amphrs.  even using 250 watts per hour (about 20 amps per hour) you should be good for 15 hrs.  It sounds like your batteries are getting tired.

Get your batteries load tested, this will show up a bad cell.
Get a good handle on how much power you are actually using.  This is pretty key in understanding these power issues.

See what others say here.  Many know a lot about this subject.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Coach Battery Staying Power

Reply #3 –
Batteries have a life expectancy usually in cycles.  Discharging from 100% to 50% and back to 100% is one cycle.  50% is about 12.2 volts. Most 8D AGM are in the 1500 to 1800 cycles.  Discharging below 50% reduces the cycle count.  Not recharging to 100% reduces the cycle count.  Limiting the depth of discharge to 75% (using 25% of your capacity) will almost double your cycle count.

    Thanks fo that Roger,  wow have I ever abused that guideline.  Every time I ran the geny when the batts were above 12.2 and every time I got up in the am and the batts were at 11.7.  Don't ever remember seeing it stated as such.  Thanks again Roger.

  Just puchased the Costco deal on 6 Lion 1200 lithium batteries. 5 day sale so I couldn't put it off.      Now I need to learn ALL about them.  It never ends....
Robert and Susan
 1995 36' 280 WTBI 8.3 3060r
 1200 watts on the roof, 720 Ah of lithium's
 Build # 4637. Motorcade # 17599
        FMCA  # 451505
        18  Wrangler JLUR

Re: Coach Battery Staying Power

Reply #4 –
Quote from: TulsaTrent –
When we stopped for the night (boondocking), the coach batteries would start losing voltage. It got so low by late night that I turned on the generator to recharge so they would not be a problem to start the next morning.

Just curious Kent.....................how many hours before they got so low that you needed to run the genset, and what if anything was consuming power?

Re: Coach Battery Staying Power

Reply #5 –
Disconnect them and watch the voltage . Maybe something is stuck on like water heater or..

Re: Coach Battery Staying Power

Reply #6 –
Quote from: Bob & Sue –

  Just puchased the Costco deal on 6 Lion 1200 lithium batteries. 5 day sale so I couldn't put it off.      Now I need to learn ALL about them.  It never ends....

The couple of big things to note on these will be that A. if you're connecting them in parallel, make sure you fully charge each one individually before you connect them as a bank; B. make sure your charge sources aren't going to run over 14.6v; and C. keep in mind that these are only 90Ah batteries, so if you have a Victron BMV or other battery monitor, you'll need to update your total capacity to 540Ah (6*90)... of course, if you have a Victron BMV you'll also need to update the charge parameters; specifically, set the charge efficiency to 99%, the Peukert exponent to 1.05, and you'll want to change your discharge floor from 50% down to around 20%.
...I'm sure other battery monitors have similar settings that need to be changed, but unfortunately I'm only intimately familiar with Victron/Sterling/Blue Sea stuff.
At a glance, though, these definitely look like decent batteries; let us know how they treat you!
Technical Support Manager and official poker of electronics at Laurel Technologies / Bay Marine Supply. Distribution and expert support of Victron Energy, Sterling Power, Blue Sea, Bussman, and Battle Born products.

Re: Coach Battery Staying Power

Reply #7 –
As Roger mentioned not having the batteries charging carefully monitored to bring the batteries back to 100% SOC after every use will shorten their life a lot. 

Other contributing inputs could be not having a battery temp charging system installed?

Foretravel equipped every unicoach with mk gels as they have the design to not be as damaged from not being fully recharged during use.

Lifeline AGM's can be carefully equalized to help restore their capacity.

A desulfurization device across the AGM batteries can maybe restore them.

Slowly.  Takes months.

A blue sea me-ACR that auto connects both banks helps lessen the need to be perfect on charging 2 separate battery.

Red tops and mk gels with temp control and having an inveter set for the gels and a auto combiner should result in 10-12 years use depending on depth of discharge of course.

I added a small solar set to keep the batteries charged during storage.

If I used AGM's they would have desulfurization devices on each battery to slow the loss of capacity
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: Coach Battery Staying Power

Reply #8 –
The other question is what kind of load do you have on your batteries?  If I turn on my magnum inverter, it will pull my batteries down to 12.0 volts overnight even if I don't have any specific load. 

Are you leaving the inverter on?  Any 120v devices pulling amps overnight?
1998 U320 40'
2005 GMC Yukon
MC# 17609

Re: Coach Battery Staying Power

Reply #9 –
Your battery Isolator could have a problem and causing your engine battery discharge.
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Coach Battery Staying Power

Reply #10 –
Stevec22 our 97 overnight with the inverter on and the aquahot on in fairly nice weather uses about 125 amp hours overnight.  12.4 volts. 

12 volts is very low
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: Coach Battery Staying Power

Reply #11 –
Quote from: Caflashbob –
Stevec22 our 97 overnight with the inverter on and the aquahot on in fairly nice weather uses about 125 amp hours overnight.  12.4 volts. 

12 volts is very low

Yeah, I wonder about my system.  Not sure where to start tracking down my amp uses, 

With smaller inverters (1-700 watt and 2-300 watt) I am still at 12,4 or so, but with magnum 2812 SOC drops a lot.  New inverter and 3 new 8D 225 amp batteries.  I may have just got crappy batteries.
1998 U320 40'
2005 GMC Yukon
MC# 17609

Re: Coach Battery Staying Power

Reply #12 –
Quote from: stevec22 –
Yeah, I wonder about my system.  Not sure where to start tracking down my amp uses, 

With smaller inverters (1-700 watt and 2-300 watt) I am still at 12,4 or so, but with magnum 2812 SOC drops a lot.  New inverter and 3 new 8D 225 amp batteries.  I may have just got crappy batteries.

Mr. Steve22 please meet Mr. Current Shunt. Wire one of these in series with your battery cable and all current flowing through this shunt will appear as a small voltage.  For the one illustrated 50 millivolts equals 500 amperes of current flow.  But!  And I mean a big but, as a rule don't try to draw more than 50% of the rated capacity of your current shunt or it will over heat.

For my needs, that is, to monitor the charging current from my 60 amp 3-stage charger, I use a 100A, 100mv current shunt and a 50 mv full scale mechanical meter.  It pegs the meter with low batteries but only for about 20 minutes.

You can get as fancy as you want from here.

Part II.  Gell cell and AGM batteries shouldn't do this but the usual failure for lead acid batteries is the accumulation of plate material in the bottom of the battery case, shorting the places to one another.  This appears as a self discharge over a relatively short period of time.

Deltec 500 Amp Shunt | 50 Millivolt Current | Northern Arizona Wind & Sun
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Coach Battery Staying Power

Reply #13 –
Please be aware when discussing battery voltage we are talking about the batteries AT REST.  So, no charging/no load for an hour or so.

Lower voltage under a high load is normal.  It is what the voltage "bounces back to" that is important in judging the batteries SOC.

And, yes a shunt and amp-hr meter is another (more expensive and more scientific) way of determining what you have used.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Coach Battery Staying Power

Reply #14 –
Quote from: wolfe10 –
Please be aware when discussing battery voltage we are talking about the batteries AT REST.  So, no charging/no load for an hour or so.

Lower voltage under a high load is normal.  It is what the voltage "bounces back to" that is important in judging the batteries SOC.

And, yes a shunt and amp-hr meter is another (more expensive and more scientific) way of determining what you have used.
I use a 3-hour rule. With real world exceptions. I ignore the current draw of the propane valve and the refrigerator and try to wait as long as possible after the furnace finishes to read the volt meter. But I always wait 3 hours after battery charging before measuring battery voltage for state of charge information.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Coach Battery Staying Power

Reply #15 –

Tulsa, I would check for a loose connection.  A loose connection can cause a discharge, instead of charging.  Is there any way your charge parameters got changed in your inverter/charger?

My Victron $206 battery monitor has been the best purchase for my charging system to date. I now can easily monitor volts, amp draw in and out, and state of charge. 

Easy to install, it comes with the shunt which easily replaces your existing shunt. The meter can go right next to the house batteries. I mounted the meter inside, however, I only use the bluetooth phone application (see pictures below, three screenprints from my phone just now).  All settings including setup can be done from bluetooth app.

Victron BMV-712 Battery Monitor Amazon.com: Victron BMV-712 Battery Monitor: Electronics

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.
97 U295 40, Build #5040, 6C8.3 325 HP
Oregon Continuous Traveler
Samsung Residential #RF20HFENBSR,
Xantrex SW2012, (3)AGM8D Hse, (2)AGM Grp24 Eng, Victron BMV-712, 1800w Solar 4 LG & 2 Sunpower
Extreme Full Body Pt w/hdlmps, new furn/floor, 4 down Lexus 2004 GX470 AWD curb weight 4,740 lbs
Prev: 1990 Barth, 10L 300 2 yrs; 91&92 Monaco Signature, 10 yrs, 10L C 300 &  6C8.3 300; 1997 ForeT 6C8.3 325 since May 2017.  Employed by Guaranty RV 14+ yrs.  Former VW New Car Dlr/Service Dlr, Sales Mgr, Rv Sales, and Service Adviser from 1968-2017
"Don't criticize what you can't understand" Bob Dylan

Re: Coach Battery Staying Power

Reply #16 –
X2 what Jack says!
Rod & Kris
Oregon
2002 U320
Build #6008
Powertech 12K