Specific Gravity and Battery Life

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feedhorn
feedhorn Solar Expert Posts: 103 ✭✭
in Off Grid Solar & Battery Systems #1
I read that if you dilute the acid in a battery, it will have less capacity (Ah), but last a lot longer. Is this true?

My last set of 4 golf cart batteries came with a specific gravity reading of 1.360 at full charge and this seemed real high to me.

I daily 25% cycle these batteries as I live full time in my motorhome. The batteries are now 3 years old and seem to be doing OK. On previous sets I usually got a one-cell failure at about this age that caused me to replace the set.

I wonder if I should dilute the acid and try and get a bit more life out of the batteries?

Any Ideas?

FH
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Specific Gravity and Battery Life

    Do not dilute the electrolyte; battery manufacturers know more about what they're doing than do unqualified "experts" handing out old wife's tales. If you do water it down, it will have less capacity but it won't last longer. If anything you'll knock years off its potential life.

    An SG reading of 1.350 is quite high. There's a couple of things that can account for that: 1). you're reading just after charging and the electrolyte hasn't "settled down" yet. They really need to sit an hour or so before you can get an accurate reading; 2). you have a cheap or otherwise defective hydrometer. No matter, as it's all relative anyway. If you take baseline readings when the batteries are new and fully charged and compare subsequent readings to that it doesn't really matter what the numbers are - it's how close they come to the "known good" reading when new; 3). somebody screwed up when they filled the batteries or sent you some "tropical" units; 4). the battery company purposefully upped the electrolyte to increase the activity and squeeze more power out of them. Oddly enough this is the opposite of watering them down, but the end result is the same - shorter life. Batteries have an optimal electrochemical balance which involves all aspects of their construction and use in order to get the most life for the intended application. Buy the right ones to begin with, maintain them properly, don't abuse them, and you can get a lot more than three years out of them. Even the cheap ones.

    (Now someone else will come along and say I'm wrong, then six engineers will join in and prove I'm right. This happens a lot. :roll: )
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #3
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    Re: Specific Gravity and Battery Life

    Yes, I've heard the same thing. Traction batteries all tend to have high SG's in order to squeeze as much energy into as small/light a space as possible.

    My forklift batts have a 1.285 SG. Most of the high quality stationary batts used around here have a 1.26 SG with a 20 year life expectancy. ....so yes, I've also thought of diluting, just haven't dared to touch my brand new batteries. Look forward to reading some of the other responses.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #4
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    Re: Specific Gravity and Battery Life

    The required SG for full charge is derermined by the manufacturer at the time the batteries are made.

    You DO NOT want to change this by diluting the electrolyte. Do not remove any electrolyte, but, I do have some cells here which run a bit high on SG, so do place more distilled water in those cells, trying to cool them down a bit.

    YES, your 1.360 SG seems very high, perhaps overcharging, of your Hydrometer is off. Have seen inexpensive hydormeters with a pointer type float, wiiht eroded floats, which have "worn out" over time.

    To me, the SG reading is very important, in absolute as well as relative terms. With a good glass float Hydrometer, is is possible to make readings repeatedly, within 5 points IMHO. This IS important. It is important to record SG readings when comissioning a battery bank, and use these for decisions as to charge settings and battery health in the future. But, Hydrometers DO break, so the ability to make absolute readings is important.

    Being a bit obsessive, I bought three Freas Hydrometers before my first large battery bank arrived. Took readings with each, and each had identical readings within my ability to read them.

    As an aside, After each SG reading session, it is important to rinse the Hydrometer with distilled water, as over time, the internals of the Hydrometer gets sticky crud on it, and can lead to false readings.

    Read the FAQs http://www.windsun.com/Batteries/Battery_FAQ.htm for pointers on taking accurate SGs.

    YMMV, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #5
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    Re: Specific Gravity and Battery Life

    Just another vote for not messing with them, Hope they last you another 3 years!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #6
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    Re: Specific Gravity and Battery Life

    Yes, lower concentration yields longer battery longevity.

    SG is a compromise between battery longevity, charging, and discharging performance.

    A lead acid battery is best designed to deplete sulphuric acid before significant structural damage is done to plates. You want the acid concentration to determine state of charge percentage. This depends on plate thickness and aging of plates.

    High SG makes a 'hot' battery with more capacity, but it's play hard, die youth.

    Just because a battery is built with lower SG level is not the only factor in longevity. Long float charge, or overcharging, will 'crack' water into hydrogen and oxygen. Positive plate is where the oxygen is created and long term exposure to being bathed in oxygen will accelerate oxidation of the positive grid resulting in high resistance that limits battery's performance, in worse case, unable to support load without collapse of terminal voltage.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #7
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    Re: Specific Gravity and Battery Life

    RCinFLA, what do you think about removing acid to reduce SG ? Would you do it to your batts if they used 1.285 SG ?
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #8
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    Re: Specific Gravity and Battery Life
    stephendv wrote: »
    RCinFLA, what do you think about removing acid to reduce SG ? Would you do it to your batts if they used 1.285 SG ?

    No, I would not. Maybe if I was using 40-50% of capacity each day knowing that cycling was going to be the determiner of battery longevity (<2 years).

    Another unknown factor on a new battery is how the manufacturer pre-formed the plates. Some manufacturers shorten the precharge time of plates. They put an initially higher SG (1.30) knowing it will drop after positive plate is fully formed after several cycles.
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  • feedhorn
    feedhorn Solar Expert Posts: 103 ✭✭
    #9
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    Re: Specific Gravity and Battery Life

    A little more info:

    Since the batteries are 3 years old and I would not feel ripped off if they failed anytime now. The batteries are Sam's Club 'Energizer' golf cart batteries. They had high SG 1.360 from the beginning and it never decreased. I checked my hygrometer and it reads accurately, so no problem there.

    It was a mystery to me, so for three years I just figured that the manufacturer had messed with the chemistry a bit. Lately, they seem to be getting sulfated more easy and it is hard to get them unsulfated. I've had to do more often equalizations to get them back working normally.

    Anyway, I decided to go ahead and dilute the acid down to a SG of 1.280 and see if I notice anything different. So far, I've noticed no difference in performance. So far as to the sulphating, I can't really tell yet.

    BTW: I do fully charge, equalize, and rest the batteries over night before taking SG readings.

    FH
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #10
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    Re: Specific Gravity and Battery Life

    If I understand battery chemistry correctly (no guarantee of that)--if the batteries are sulfating, the specific gravity of the electrolyte should be going down as the sulfur that was in the acid is now permanently bonded to the lead as crystalline lead sulfate.

    Perhaps you have some other problem... Do the cells look "bulged out" or the positive battery posts look like they are "extruding out of the case"? Something like that may be plate or plate grid oxidation. Another, irreversible problem. Plate and positive grid oxidation can be accelerated by excessive equalization.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
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    Re: Specific Gravity and Battery Life

    Bill, do you need another cup of coffee? :p

    His batteries inexplicably read 1.360 (possibly inaccurate hydrometer) so against all advice he's added water to knock the SG down to 1.280 (more along the lines of what you'd expect on brand new batteries, as RC indicated).

    The only immediate effect will be a reduction in the maximum amount of Amps that can be pulled as the capacity of the batteries is now reduced. The long-term effects may not show up for years, if then as batteries can last quite a long time with proper maintenance.

    The quite likely possibility of doing the re-mix wrong and suddenly having very dead batteries with no more lifespan seems to have been averted. But the warnings still hold; it's a bad idea to muck about with battery chemistry as there is much greater chance of doing damage than realizing any practical gain.

    Bill's got the bit about SG going down over time as the sulphur adheres to plates spot-on. This is one of the reasons behind the notion that dilution may shorten life rather than extend it; if it's meant to start out with 1.280 and last for seven years with the SG dropping down to a maximum potential of 1.250 then cutting the SG down to begin with may cause a severe and perhaps sudden drop off of capacity at some point in life.

    I'd be suspicious of that initial reading. But don't anyone listen to me; I've got a dozen batteries stockpiled to go to scrap right now - every one of them abused by people who didn't listen to me, and probably still won't. Mine are fine, btw. :roll:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #12
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    Re: Specific Gravity and Battery Life
    Cariboocoot wrote: »
    Bill, do you need another cup of coffee? :p

    Marc, you do have me confused... :confused::confused:

    I looked at my post and did not see anything strange there (stupid or smart typos, etc.:p).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #13
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    Re: Specific Gravity and Battery Life
    feedhorn wrote: »
    Since the batteries are 3 years old and I would not feel ripped off if they failed anytime now. The batteries are Sam's Club 'Energizer' golf cart batteries. They had high SG 1.360 from the beginning and it never decreased. I checked my hygrometer and it reads accurately, so no problem there.

    SG of 1.36 is so high I find it a bit hard to believe. I would question hydrometer accuracy.

    Highest I have seen in a new battery is 1.31
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
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    Re: Specific Gravity and Battery Life
    BB. wrote: »
    Marc, you do have me confused... :confused::confused:

    I looked at my post and did not see anything strange there (stupid or smart typos, etc.:p).

    -Bill

    Paragraph #1: you're uncertain when you're absolutely right.
    Paragraph #2: nothing in the OP's posts denoting problems; just wondering about extending life of batteries by watering down (suspiciously high) SG.

    My problem is I don't drink coffee. Anyway, that's my excuse and I'm sticking with it. :p
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #15
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    Re: Specific Gravity and Battery Life

    The second paragraph was a comment about "sufates" causing problems--but yet the s.g. remained the same over these three years. So, did not sound like sulfating was a problem (yet).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • feedhorn
    feedhorn Solar Expert Posts: 103 ✭✭
    #16
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    Re: Specific Gravity and Battery Life

    Little more info:

    I've been watching batteries charge and discharge every day for the past 9 years and I can feel sulphate in my bones. Sulphate first appears to me when batteries won't take a high current during bulk charging.

    Some History:

    My first set of new batteries were gone in one year due to chronic undercharging. What a dummy...

    My next set died in 3 years due to a bad battery cable that caused two of the set of four to do all the work and just wore them out. I then got a clamp-on DC amp meter and found the bad cable.

    This set worked great until I started using the battery power to heat my coffee water (drawing 150 amps off the set for about 3 min) some six times a morning. They have really never recovered from this abuse. Cells got badly mismatched.

    I have learned that batteries do work best when you don't use them. They just like to be full, floated, and unused. Like you find in most RV's that stay plugged in all day.

    I have also learned that batteries must be fully re-charged every day with even a few +Ah of overcharge too. Now this can be hard to do using solar power on short winter days. Here is where doing bulk charge with a generator comes in handy.

    I figure the set of batteries I got now will complete 4 years of service for me and that will be a record.

    FH
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #17
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    Re: Specific Gravity and Battery Life
    feedhorn wrote: »
    I have learned that batteries do work best when you don't use them. They just like to be full, floated, and unused. Like you find in most RV's that stay plugged in all day.

    Not true of all batteries. Certainly so for automotive/RV/Marine types, but the "motive force" (traction) batteries that are a mainstay of RE actually prefer to be cycled.
    I have also learned that batteries must be fully re-charged every day with even a few +Ah of overcharge too. Now this can be hard to do using solar power on short winter days. Here is where doing bulk charge with a generator comes in handy.

    Daily recharging certainly is preferred by almost all standard lead-acid batteries. Not sure what you mean by "a few +Ah of overcharge". Overcharging is either too much Voltage (particularly hard on AGM's) or too much current or maintaining Absorb Voltage for too long. No battery wants that kind of mistreatment.
    I figure the set of batteries I got now will complete 4 years of service for me and that will be a record.

    FH

    Well you've done most of the things that result in premature battery death. Want to try some of the others? :p Four years is pretty short life still, by my experience. But you're getting better all the time, right? :D
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  • feedhorn
    feedhorn Solar Expert Posts: 103 ✭✭
    #18
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    Re: Specific Gravity and Battery Life
    Cariboocoot wrote: »

    Not sure what you mean by "a few +Ah of overcharge". Overcharging is either too much Voltage (particularly hard on AGM's) or too much current or maintaining Absorb Voltage for too long. No battery wants that kind of mistreatment.





    By overcharging, I mean that batteries are not 100% efficient at re-charging so if the Ah meter says you have removed say 100Ah then you need to put back in maybe 110Ah to fully re-charge the battery.

    FH
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #19
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    Re: Specific Gravity and Battery Life
    feedhorn wrote: »
    By overcharging, I mean that batteries are not 100% efficient at re-charging so if the Ah meter says you have removed say 100Ah then you need to put back in maybe 110Ah to fully re-charge the battery.

    FH

    That is absolutely true. Batteries are only about 80% efficient so you will "use" 20% more Amp hours to charge than you'll get back. What battery monitor are you using? The better ones can be programmed for charging efficiency (if known for the battery) so when it's at 100% it really is 100%. They go off over time, of course, as capacity inevitably decreases.

    If there's one thing the industry needs it's better batteries - that are affordable.
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  • feedhorn
    feedhorn Solar Expert Posts: 103 ✭✭
    #20
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    Re: Specific Gravity and Battery Life
    Cariboocoot wrote: »
    If there's one thing the industry needs it's better batteries - that are affordable.


    Amen to that ! I'm anxiously waiting for surplus Li-Ion batteries from the electric car industry. Some frustrated RV'ers might even steal an elf for its batteries.


    I have a Xantrex Link 1000 Ah meter but the keyboard got static damaged and I can no longer change any of its settings.

    FH
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #21
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    Re: Specific Gravity and Battery Life

    Being a coffee-aholic in the AM :grr I know how you want that extra cup of java.... BUT it you were to go propane and use a larger coffee pot, I think you will enjoy the luxury of longer battery life:D:D That heavy concentrated draw will have a cumulative effect... never mind the withdrawal...

    I have to ask 5 Inverters???

    what else are you running other than that 46 " LED and the Sat internet?

    ej
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • feedhorn
    feedhorn Solar Expert Posts: 103 ✭✭
    #22
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    Re: Specific Gravity and Battery Life
    westbranch wrote: »
    Being a coffee-aholic in the AM :grr I know how you want that extra cup of java.... BUT it you were to go propane and use a larger coffee pot, I think you will enjoy the luxury of longer battery life:D:D That heavy concentrated draw will have a cumulative effect... never mind the withdrawal...

    I have to ask 5 Inverters???

    what else are you running other than that 46 " LED and the Sat internet?

    ej

    0. I have one big 2000 watt inverter but its very inefficient on light loads and it makes noise too. Now just for microwave use and power tools.

    I use various little inverters in various locations around my rig.

    1. 100watt for keeping my laptop going 24/7 so it can wake out of hibernate automatically.

    2. 250 watt by the bed to run my electric blanket and bedroom sound system.

    3. 150 watt by drivers station to run laptop map program while driving.

    4. 750 watt to run refridgerator on excess solar power.

    5. 200 watt USB controlled inverter to run satellite modem and other USB devices.

    Thats about it.

    FH
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #23
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    Re: Specific Gravity and Battery Life

    It may have been something to cover their butts, but once I was witness to a automotive battery explosion and the reason Interstate gave was that the battery had too much water and the mixture was off. It may have been an extreme mismatch, but it wasn't a pretty site to see a 220 pound guy get knocked on his butt when it happened. So please be careful and if you decide to go that route, do it a little bit at a time.
    It burned his throat and lungs. He was lucky he was still a couple of feet away when it happened.
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