Battery Cycling and Life - Fiberglass RV


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Old 10-12-2014, 11:52 AM   #1
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Battery Cycling and Life

I was reviewing the settings and history statistics on my battery monitor because of a high number of high voltage alarms. It seems I had it set too close to the nominal value for the highest charge voltage. I've never seen the voltage exceed that value, so I presume it was entirely a programming error on my part.

I also reviewed the battery specs in the course of this process and discovered one error in the temperature compensation. I left it at the nominal value which was a percentage of AH capacity, while the battery spec was in millivolt/deg C. I did a little math an reduced my temp compensation significantly. I don't think this is a huge factor because my batteries are either charging or discharging most of the time and that keeps the temperature in the typical range in cooler temperatures. Temps are higher in the summer despite the lower loads. I plan to add some 1/2" spacers between the batteries for better cooling in warmer temperatures.

212 DAYS OF RECORDS.

Average Discharge (AH): -57.3 AH
Avergaer Discharge %: (recalculated after ea. sync): -14.9%
Deepest Discharge (AH): -286 AH
Deepest Discharge (%): -74.9%
Total AH Removed: 8049 AH
Total AH Charged: 9873 AH (temp compensation explains difference)
Number of Cycles: 20
Number of Sync's: 93 (A sync means the battery was fully charged)
Number of Full Discharges: 0

Noteworthy, is the one time I left my refrigerator on AC using the inverter. It ran my battery down until the alarm sounded. This is one reason I want to switch to a Danfoss type compressor DC fridge when my fridge starts to give out.

During this time my batteries have only "cycled" about a dozen times. In actuality they cycle a small amount every day. I am guessing the definition of a cycle is 50% or greater discharge. I don't know how they count cycles, but obviously it is of little value to me if the number is so low. We know that discharging less than means longer life. One of my friends lives in an RV. He went overboard on capacity and his batteries rarely discharged more than 25% and lasted 11 years. He paid a big penalty in weight, and is generally carrying an insane amount of weight for a 350 motor. He's blown the motor in his RV three times.

Below is a good example of battery life in a stationary application:

Battery life is twice as long if discharged to 25% compared to 50% discharge. But if they in an RV, you are carrying around all this extra weight. Is it better to change batteries every three years or every six for someone who daily cycles batteries?



Based on this, if I keep my discharge numbers at 15% I should get more than 3000 cycles out of them. Possibly 10 years of life.

One of the reasons I'm a huge fan of solar panels and solar charging, is it keeps the batteries topped up and maximizes their life. People forget to charge batteries. Prompt charging (daily in the case of solar panels) is the best method, IMHO.
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Old 10-25-2014, 10:55 AM   #2
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This was an interesting week. I had four days of overcast and rain. My batteries were reduced to the second lowest state of charge I've had in my camper since I installed my solar panels. Each day I saw my state of charge drop. I normally shut off my inverter during daytime, except in the middle of summer where I have so much power I leave it on. With minimal loads it draws 2 amps, with my entertainment system on, it draws as much as 8 amps. I was using it overnight to transfer TiVo recordings so I have a stockpile of TV for future rainy days.

While it was raining I saw only 2 Amps coming in and a small discharge when I ran my inverter. I decided to continue using power freely, for TV and Internet, electric blanket, furnace and lights. I wanted to see how it would do with a heavy load to simulate more challenging conditions. Because I had not exceeded 100 AH draw (75% state if charge ). Today is is finally clear and calm and my panels are cranking in almost 18 amps at 1030 am.

I was thinking, will I have enough panels once winter hits and how can I add more panels?

I have been running my furnace to warm up my camper and then shutting it off, and relying on my electric blanket to stay warm, although last night I left my quiet furnace on and dialed the blanket down to minimum. Wintertime use my electric needs would increase obviously.

10:41 hours of daylight today drops to 9:04 hours on the winter solstice. That is only. 85% the light we have today.

I decided that I could add two more panels to the front of my camper.
There is an angled face that is nicely aligned with low winter sun angles. This angle would be just about optimum for wintertime at my latitude

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These panels would be of benefit in the winter if facing south and of benefit in the early morning or late afternoon anytime, if facing east or west respectively. They would not overload my charge controller in this configuration. Flexible panels would be ideal in this situation. From what I've read industrial Velcro is the best way to attach them. I'd worry about branches catching on the wiring. I suppose I could tape the wires down with shrink wrap tape.

I considered adding a pair of connectors at the back of my camper for external charging. I even checked prices of panels at Home Depot and discovered prices had gone up dramatically. Fortunately solar panels are still reasonable at Amazon. An external pair of panels would be awkward to store but I could probably rig up a way to carry them on my roof rack. They would require me to update my charge controller to a larger 60 amp one if I used them in the summer. Or I could store them in the summer.

My system seems to be performing well as it is. So I may do nothing. If the weather was really bad for several days and I used the furnace constantly I might find myself wishing for more power. At some point I'd like a larger inverter so I could distill water, run an induction cooker, and a satellite TV receiver.




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Old 10-25-2014, 01:03 PM   #3
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hey thanks Nightsailor....and timely.... (LONG)

while I can't gather the detail information you have....I have tried to get a feel for my usage and recharging capacity with a panel meter I installed....and it's been inetresting /fun....like a new hobby

I have come to the conclusion that it would not cost very much to fill all my power needs with solar, especially at today's prices and the predictable sales "cycles".....just like buying lawn mowers in the fall....so far, I have found that buying panels in oct/nov can be done at very attractive prices...around here anyways...

I started with a 40W panel last fall that I rigged/connected as a deployable panel (on or away from the trailer...stored inside when not in use).....reasons for this were many....park in the shade?, point any which way for max exposure, anxiety of drilling holes in roof, fear of mounting in a "wrong" place, sell the trailer/have to sell the panel with.....yeah, lots of reasons...

After one full year, now I know I'm going to have this reailer for a long time....I also know that most often I only stay in one spot for one night so I'm "on the road" in the middle of the day (prime recharge time)

I've been thinking of having two panels, one on the roof in addition to the one I have would serve my needs best...I think...I came up with a rather painless way of doing it....yesterday, with this in mind I went back to the same store where I bought the first panel (after one season I'm very happy happy with it) just to look.....and lo and behold the same panel was again on sale for 50% off !!!! (just like last year at this time)....so I had to get it

so my plan is to fasten two suction cup type glaziers tools to the panel (one as shown at both ends of the panel, bolted or riveted to the aluminium frame) place/mount it on the roof near the fridge vent, run the wire down into the fridge control compartment, install the simple controller there and connect the wires to the 12V block in that compartment (that feeds power to the fridge)....

I've used that particular suction tool for two summers to secure kayaks to the roof and found it super secure....nuttin' is gonna get these things off once they are on (put on a wet, clean surface)

the controllers that come with these panels are sized to accept two panels if need be (panels put out 3 amp max, controller is 7 amp)

so what I'll end up with is one panel on the roof with no permanent mounting issues/headaches....should I sell I could just take the panel with me...if I park in one spot for a long time (like a week) I could take the roof panel off easily and position it better, either on the roof or away from the trailer (connect it to my deployable panel controller mounted in my propane locker).....as a side benefit too, now I have TWO 15' extension cords/wires for use with the deployable

can't wait to rig the system up and try it out....my power use if a fraction of yours....I'm going to be power "rich" when this is done

cheers and thanks for all the info...
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Old 10-25-2014, 05:17 PM   #4
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Great thread. The last of my solar bits has arrived and I have about figured everything out to get it mounted on the Scamp. Next month I will buy a couple of 6V gold cart batteries and between the holidays I should get it all hooked up and running.

NS, that is an interesting chart, I have not seen it before. It seems to dispel my notion (gathered from the net) that a 50% discharge rate is somehow a "maximum" to design to. The curve actually "breaks over" so to speak at 50% and it is much better from a battery life standpoint to design for 30% or 40% (or less). Conversely, if you are running at 50% and occasionally run down 60% or 70% you don't loose as many cycles as if you ran at 20% - 30% and go to 40% or 50%. Although in reality, I suspect that for the occasional week here and there I will be doing until I retire the age of the batteries will have more to do with their life than the actual use I put them too. I may run two batteries now and four when I retire and do more long terming. Thanks for the info.
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Old 10-25-2014, 06:17 PM   #5
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OMG, READ... I first read this thread as BICYCLING and LIFE. Sorry I really need to pay attention
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Old 10-25-2014, 07:24 PM   #6
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Conrad, I applied two 100 watt flexible Renogy panels to the front of our Lil Snoozy with 3M outdoor VHB tape, and protected the wires (hid them) within plastic computer and TV wire looms.
Dave & Paula
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Old 10-25-2014, 11:29 PM   #7
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Funny, Wolf....

I was just starting to think the other way.....like maybe I should have bought/installed ONE group27 batt instead of the TWO GC batts and invested the difference in more panels.....less weight (those GCs weigh a ton!)

I dunno.....if I was on the ball as much as Conrad I could calculate my max night usage and figure out how many panels it would take to produce that in, let's say, 8 hours.....might be possible....but I got the batts now anyway so it would just be for "fun"

went looking for you in the registry as we seem to be "on the same page" sorta....but couldn't find ya.....too bad, would like to see your rig/set-up....cheers, F
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Old 10-26-2014, 06:41 AM   #8
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Quote:
Originally Posted by David B. View Post
Conrad, I applied two 100 watt flexible Renogy panels to the front of our Lil Snoozy with 3M outdoor VHB tape, and protected the wires (hid them) within plastic computer and TV wire looms.

Dave & Paula

I have been reading about the industrial Velcro and many people write that the adhesive doesn't hike up. I don't want to remove them. A permanent mount is best for my application. People have told me how well the 3M tape holds up. I think your methods make the most sense for attaching flexible panels


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Old 10-26-2014, 06:48 AM   #9
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Quote:
Originally Posted by Franswa View Post
I was just starting to think the other way.....like maybe I should have bought/installed ONE group27 batt instead of the TWO GC batts and invested the difference in more panels.....less weight (those GCs weigh a ton!)

I dunno.....if I was on the ball as much as Conrad I could calculate my max night usage and figure out how many panels it would take to produce that in, let's say, 8 hours.....might be possible....but I got the batts now anyway so it would just be for "fun"

went looking for you in the registry as we seem to be "on the same page" sorta....but couldn't find ya.....too bad, would like to see your rig/set-up....cheers, F

I figure my two batteries will last as long together as if I bought two single batteries that lasted half as long. I could not make my mind up which way to go. The weigh penalty is significant. My uncle convinced me to go with two and now my camper sags a bit on that side from the weight of the batteries and water tank. I do take comfort that I can tolerate heavier loads.

The one device I like best is my battery monitor and just bought another for my boat. I like having an accurate idea of what's going in and out of the bank. Is it needed? Probably not but I find it interesting to study and understand how much power I make in varying weather conditions.

I'll try to figure out what the registry is .


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Old 10-26-2014, 07:43 AM   #10
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I understand the weight penalty of going to two batteries, that is but one of the reasons I removed the second propane bottle and heavy dual bottle mount from the tongue. I will still be at a deficit as the second battery is heavier than the second propane bottle but I have a new 3500 lb axle on the Scamp and tow with a 1/2 ton pickup (500 lb tongue weight limit) so it is not a problem.
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Old 10-26-2014, 08:05 AM   #11
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It is comforting to have extra capacity but if you don't need it, keeping things light is very cool. Perhaps a lithium battery would work for you. If you go that route Victron has devices to prevent overcharging that can be installed on the battery.


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Old 10-26-2014, 09:27 AM   #12
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Somehow, unless someone was planning an orbital sojourn, I doubt if the extraordinary cost of a lithium battery would ever be recovered from weight saving improvements, real or imagined.

Can't say I have ever heard of one being used in an RV as a primary battery, unless maybe those mega-buck RV's use them.

Wait.... Maybe there will be a Tesla Trailer.....LOL
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Old 10-26-2014, 09:44 AM   #13
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Smart Battery makes a 12v drop in replacement battery that is Lithium Ion. The electronics to protect it are on-board the battery. A 100ah Group 31 type battery is around $1300, but they are supposedly good for 3-5000 cycles, so over the long haul may be worth the price. The good thing is it's truly drop in with no changes needed for your charger or converter.

12V RV Batteries | Deep Cycle Lithium Ion Batteries | Smart Battery
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Old 10-26-2014, 10:53 AM   #14
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Smart Battery makes a 12v drop in replacement battery that is Lithium Ion. The electronics to protect it are on-board the battery. A 100ah Group 31 type battery is around $1300, but they are supposedly good for 3-5000 cycles, so over the long haul may be worth the price. The good thing is it's truly drop in with no changes needed for your charger or converter.

12V RV Batteries | Deep Cycle Lithium Ion Batteries | Smart Battery

I am not sure these have a disconnect feature to prevent overcharging.


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