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Topic: Battery Lifespan Question (Read 510 times) previous topic - next topic

Battery Lifespan Question

Here is a question for our Forum battery experts.  We have two of the highly recommended O'Reilly AGM8D batteries in our coach (house) battery bank.  They were installed 2 years ago, and are working fine.

When not on the road, we park our coach in our driveway, where I have a 50amp RV-type electrical outlet.  I have always kept the coach plugged in at the house, because we have a residential refrigerator which must be continuously powered.  Lately I have been wondering if this is the best policy, in terms of optimizing battery life.  While plugged in, of course, the batteries are kept at 100% charge by our Magnum charger/inverter.

We also have solar panels on the coach,  and they can easily keep the batteries charged when parked at the house.  I have tried unplugging the coach for several days at a time, under different climatic conditions.  Running the fridge (off inverter), several night lights, the HWH panel (I leave auto-level activated when parked), smoke and propane detectors, etc. the batteries usually draw down to about 70% overnight.  The next day by around noon they are fully charged back to 100%.

I have read that batteries have a finite number of 100% discharge/charge cycles, and once you use those up, the battery is dead.  If I unplug the coach, and let the solar panels take care of battery charging, I am saving money on my electricity bill AND we are getting some use out of our investment in the PV system.  However, I am also putting the batteries through repetitive daily discharge/charge cycles.

So my question: is it better (in terms of optimum lifespan) for deep cycle batteries to be constantly held at 100% charge for extended periods of time, or is it better to "exercise" them on a daily basis through discharge to 70% and then recharge to 100%.

I'm not worried about the cost of electricity when keeping the coach plugged in.  I would like to extend the useful life of the expensive (and hard to change out) batteries as much as possible.

What's the verdict?
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Battery Lifespan Question

Reply #1 –
Chuck  ----  There are some posts on the forum relative to batteries, chargers, etc.  Bottom line :  Check your charger tech. spec's and see if it has de-sulphating capability.  Sulphating is a battery killer over time.  It sounds like you would be much better off if you have that capability in your charger.  I have deep cycle golf cart batteries in series/parallel which were in the machine when I got it about eight years ago and they are still doing OK .  I do plan to change them out before our next extended trip.    Have a great day  ----  Fritz
Fritz & Kathy Johnson
1991 36'

Re: Battery Lifespan Question

Reply #2 –
Chuck, I will stick my kneck out and just say that as far as cycle duties with Battery life expectancy is concerned it is based on  more like a 50% discharge not so much the 70% as you mention. I do have a question on your Res fridge though. If you are parked at home and not taking coach away for a trip, why are you keeping it on and therefore using power to recharge and also "using up part of their so called life"??
I have ours off all the time unless we are going away, but do leave doors ajar on 'fridge. I also have 900+ watts on roof so charging would not be a problem and we have lots of sun here during the year.
JohnH
Coachless, now use aircraft. 2003 Ford Travelair TC280 class C. Super shape. Just for 1 yr .
1994 Ford E350 ClassC,total renovation inside and out. Now sold.
2000 U295  36' Cummins 350 c/w Banks Stinger, Resonator upgrade,Solar, LED lites.Residential fridge with slide out pantry. Build 5674. Sold
ex 92 GV 022C ored Cummins. Sold
ex 95 GV240 cat 3116. Sold
2017 Mini cooper s & 2016 land Rover LR2 HSE  LUX.
jhaygarth@aol.com    SKP #130098
treat everyone as you would like to be.

Re: Battery Lifespan Question

Reply #3 –
Chuck,
here is Don's thread that pertains to your battery type.

AGM Battery Homework

Some of the people seemed to think that the O'Reilly battery was just a rebranded MK Deka so I attached some links about that battery.  It looks like the expected lifespan of your batteries with a daily drop down to 70% DoD would be around 1700-1800 cycles (or about 5 years). 

I don't think it would be a particularly good idea to exercise the battery on a daily basis like that if you don't have to. 
Robert
Build # 5304
1998 34' U270 Cummins 6CTA8.3

Re: Battery Lifespan Question

Reply #4 –
Quote from: fkjohns6083 –
Check your charger tech. spec's and see if it has de-sulphating capability.  Sulphating is a battery killer over time.  It sounds like you would be much better off if you have that capability in your charger.
Our Magnum MS2812 does have a "de-sulphating" mode.  However, the tech at AM Solar did not turn it on...he said in their opinion the AGM batteries did not "like or require" the de-sulphating procedure.  I bowed to their experience level on that one, but I may do some research on my own to see if I still agree.  If I wanted to use it, it is a simple change to the charging program.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Battery Lifespan Question

Reply #5 –
Quote from: John Haygarth –
I do have a question on your Res fridge though. If you are parked at home and not taking coach away for a trip, why are you keeping it on and therefore using power...
Our (in-house) fridge is just like our garage - it never seems to be "big enough".  When we run out of room in the house cooler, we use the RV fridge for our "overflow".  Right now it's full of frozen steaks and pizza (two of my favorite food groups).  I also like to keep a few 6-packs chilling out in the coach, so when I'm working out there I have quick access to a "Cold One".
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Battery Lifespan Question

Reply #6 –
Quote from: rsihnhold –
I don't think it would be a particularly good idea to exercise the battery on a daily basis like that if you don't have to.
I seem to agree...  I just wanted other opinions in case I was way off base.  The coach is plugged back in now.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Battery Lifespan Question

Reply #7 –
Bottom line with AGM's is all you have to do is properly program your smart inverter/charger and leave it plugged in.

Period.

And desulfating is more for wet cells, NOT AGM's.
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: Battery Lifespan Question

Reply #8 –
We've got a "True Charge" that keeps track of both sets of batteries and works well. In our experience, every 5-8 years, get fresh batteries. No charger/indicator that I know of, will tell you which one of the batteries is going south. My neighbor, after being at the dock for six months, went to start-up and nada. Hit the boost and double nada. I missed the fun, but a nice guy had a boost charger, hit the coach battery that the VOM proved was doa and after a few minutes, bingo! In my limited (30 years experience), replace ALL batteries when one goes south.  ^.^d
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: Battery Lifespan Question

Reply #9 –
Our coach is currently in storage with no shore power hookups, and the Danfoss compressor based marine fridge is on all the time (providing some aux food storage). Currently, I have 408 watts of solar hooked up, and with the 4 O'Reilly 8d AGM house batteries (not counting the one 8d AGM chassis battery), overnight it is usually at about 96% in the morning. So less than a 10% depth of discharge. My research leads me to believe that number of lifetime charge cycles is inversely proportional to depth of discharge per cycle. 50% depth of discharge is just the the number used by most to evaluate the practical life span of deep cycle batteries for a given application. The cheapest way to have longer battery life is to use less energy, thus making the conversion to LED lighting a no brainer, as is adding solar to offset the daytime use of energy and hopefully, keep the batteries at 100% at nightfall (for dry camping of course). I will be adding another 500 watts of solar, but since we needed new house batteries, decided to do the four AGM 8d upgrade (Installing 4 batteries and a busbar setup in a 99' 36 foot U270) before adding more solar, as it is best to have all batteries as close to the same age as possible. So far, the system is working great.
Don
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Don & Tys
1999 U270 3602 WTFE #5402
Xtreme Stage 1 w/Headlight, Step Conversion, etc.
2009 Honda Fit Sport with Navi
Freedom is NOT "just another word for nothing left to lose"... with apologies to Kris Kristofferson