Battery voltage drop question

mfoobar
mfoobar Registered Users Posts: 13
Hi all,
Just joined your forum... seems like loads of good information here. I'm actually in England, but (despite what people say) we do occasionally get some sun here too ;)

My first question:

If you had a single 12v battery of around 110Ah, that was in good health and fully charged and rested with a terminal voltage of 12.80v. What would you expect the voltage drop across the terminals to be if you applied a simple 4A load (e.g. 12v headlight bulb). ie. if you waited for the voltage to settle, after say, 5-10 minutes. What would you expect the voltage across the terminals to now be (with the load still on)?

Thanks!

-Matt
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Comments

  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Battery voltage drop question
    mfoobar wrote: »
    If you had a single 12v battery of around 110Ah, that was in good health and fully charged and rested with a terminal voltage of 12.80v. What would you expect the voltage drop across the terminals to be if you applied a simple 4A load (e.g. 12v headlight bulb). ie. if you waited for the voltage to settle, after say, 5-10 minutes. What would you expect the voltage across the terminals to now be (with the load still on)?

    If that ware my batteries, I would expect 12.4-12.5. However, I guess every battery is different.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery voltage drop question

    Welcome to the forum!

    It is difficult to make a general statement as lead acid batteries are very sensitive to temperature, loads, and time...

    You should probably only see a couple 1/10ths of a volt drop with that small of load, and it may even rise a bit over time after the load is applied.

    Looking at voltage setpoints... For a "resting" battery with no loads (for the past 3+ hours), a 50% discharged battery will read around 12.0 Volts. And as a sanity check--We recommend that you do not load a 12 volt battery lower than ~11.5 volts (excluding surge current to start pumps, etc.).

    Several things happen if you discharge a battery too much... First, it can damage the plates/chemistry of the battery to pull it near dead. Second is that lead acid batteries can have a 20% variation in capacity between individual cells--5 cells could still have 20% state of charge, and the 6th cell could be at 0% SOC, and actually begin to "reverse charge" -- Which is a killer for pretty much all rechargeable battery chemistries.

    Lastly, the longer a battery sits at less then full charge, the more lead sulfate "hardens" (crystallizes) which permanently reduces the battery bank's capacity. In general, you don't want a partially discharged lead acid battery to remain below (call it 75% SOC) for more than a day (or couple days) before recharging back over 90% SOC.

    If you are interested in monitoring the charge on a lead acid battery... There is the Hydrometer to measure specific gravity of the battery. It is the "gold standard" for monitoring charge/state of battery. Of course, you cannot do this for sealed (AGM) and GEL cell type batteries.

    Battery Monitors (Victron is a good European brand) are a nice tool. You put a shunt in the battery lead and the monitor records current flow (and direction) over time. It does a pretty good job of estimating battery state of charge--Sort of like measuring the amount of fuel in a car's gas tank by measuring fuel flow out of / into the gas tank. But, they do have "errors" and you need to understand those limitations and how to "re-sync/reset" the Monitors (basically the battery bank has to be recharged back to 100% SOC every so often to reset the monitor to 100% too).

    A couple of good FAQs to read:

    Battery FAQ
    www.batteryfaq.org

    To give you an idea of the the battery "curves":
    BB. wrote: »
    New poster "leaf" has a really nice set of charts that compare battery voltage against different rates of discharging and charging (as well as resting voltage readings).
    leaf wrote: »
    Am trying to upload the charts I am using...

    Attachment not found.Attachment not found.

    attachment.php?attachmentid=3655

    attachment.php?attachmentid=3654

    I don't quite a agree with the resting voltage line (I think the voltage is a bit low)--But it shows how to estimate a battery's state of charge while operating.

    Note, where the charts "flatten out"--the room for error estimating state of charge is pretty high.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Battery voltage drop question
    NorthGuy wrote: »
    If that ware my batteries, I would expect 12.4-12.5. However, I guess every battery is different.

    That's right. :D
    Given a good battery of 110 Amp hours @ 12.8 Volt "full charge" plus a 4 Amp draw and assuming good wiring & connections as well as accurate V taking at the battery, about 12.5 Volts would be expected.

    That doesn't mean that's what you'll get, though. That's why there are tolerances.
  • mfoobar
    mfoobar Registered Users Posts: 13
    Re: Battery voltage drop question

    Right, OK time to clean a bit then.

    I deliberately left the question a bit vague and theoretical as I didn't want to cloud anyones answers with too much specifics ;)

    So it seems that people concur that 12.4 - 12.5v is acceptable with a 4A load. That equates to a 0.3 - 0.4A voltage drop. Which according to the marvellous Mr Ohm means a resistance of 75 - 100 milliohms.

    So, am i fundamentally missing something, as most places I've seen internal resistances for lead acid batteries quoted as under 10 milliohms... normally around 4-6 milliohms.

    The full story... I have a bank of 3 x 115Ah 12v sealed (maintenance free) batteries in my motorhome. Yeah, yeah, yeah... I know... I used to have conventional top-uppable batteries, but when a cell died on them and I needed to replace the bank I needed to go cheaper and got suckered in to the marketing that these batteries could do an 'amazing' 500 cycles, vs 300 for normal leisure batteries. I was working on the basis they were half the price of T-105s or similar and thought I should get at least half the lifetime of T-105s with them. I also didn't have the room for 4 x T-105s so would have to have gone for 2 of them, and that wasn't going to be enough capacity. When these batteries die I *will* be going for T-105s/CR-225s. I have a single 64W solar panel on the roof, and solar prices have tumbled since I bought y panel 5 years ago, so could probably get an additional 120W panel on the roof for 184W total and so can use a smaller battery bank.

    These batteries have been 'feeling' a bit down lately. They just seem to struggle under load. I don't have a mains charger and wildcamp (boondock) most places. The batteries are charged via a 50A Sterling B2B (DC-DC) charger from the engine alternator and the 64W panel via a Stecca PR3030 charger. I've got a feeling that the batteries have often been deficit charged. Or rather that they have been getting incomplete charge cycles. As I only do a few hours driving at a time I think they've been getting lots of short bulk charge cycles and never making it on to absorption. The solar panel then just keeps it on float... and in the UK winter, not even that at the moment! The batteries happily sit at 12.8v when rested, but I think that still might be a surface charge, even though it bounces back up to that after a while of being on a load.

    The batteries are 2.5 years old, and the van is driven almost daily, but only actually used for camping in a few weekends a year, and done two 2-week trips in it since these batteries are in there. I've always been careful not to take the batteries down below around 12.3v (open voltage) and they've only been down below about 12.5v a couple of dozen times.

    So i was under the impression that I should get less of a voltage drop on load than I'm currently getting. As the batteries have been kept charged (well... as charged as I said above) they shouldn't be sulphated. I have however just found out about 'antimony free effect' and how on sealed lead acid batteries with Calcium in the plates that sometimes an oxide can form which can give increased resistance and make the batteries harder to take a charge.

    I'm actually in the process of building my own battery monitor based on an Arduino, and blogging about my experiences here:
    http://opensourcebatterymonitor.blogspot.co.uk/

    The idea is to have something that can log current and voltage to an SD card so I can get a better picture of long term health of the battery bank. If i had this a couple of years ago I'd probably have realised my charging cycle is not helping them. I can then graph the results to get a better picture of what is going on. I'm also looking to extend it to be a PWM solar regulator as well. My Stecca can't go as high as 14.8v which I would need for the T-105s. My Stecca is also a couple of meters from the battery bank and all my loads run through it (it counts Ah and has a LVD) so I think its idea of the actual terminal voltage of the battery is pretty fictional! Having read Bob's solar/battery rant I can see plenty of improvements to my setup.

    I've currently taken one of the batteries out of my van to try and run a few tests on it to see how it responds. But I'm trying to ascertain what you all think is 'normal' in terms of voltage drop. I've just given it a charge of up to 15.1v for a few hours, which got it bubbling a bit and I've just bought a desulphator and put that on the battery. I know they are a contentious topic on here from that I've read. But it cost me less than $20 and thought it might help with the calcium battery oxidation issue.

    So i know it is not the setup most of you would go for, and I would do it differently if I did it all again.. but just wanted to get your thoughts on the battery situation as it currently stands. It would be great to eek another 6-12 months out of these batteries it I can. Or at least learn as much as I can to try not to make the same mistakes again!

    -Matt
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Battery voltage drop question

    some quick comments, that 64w panel is only good for about 4% of one (1) batteries capacity, not 3, under the recommended minimum charge capacity. 5% min better at 10%
    you should look to see if you can find 2 or 4 more of matching panels(within 10% of V and amps) to be able to expand your array.
    Recommend you get an MPPT CC (or several matching pwm CCs )
    you should charge as per the manufacturers spec, don't just pick any voltage or you will knacker them... AGMs are picky!
    Yes you have been deficit charging them and now paying the price, its not the batteries fault when they are under fed...sorry.
    You should get a good 3 stage charger and charge each one separately and hope its not too late.

    Read this doc on Charging AGMs (VRLA) http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf It will explain lots about AGMs

    hth
     
    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
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Battery voltage drop question
    mfoobar wrote: »
    So, am i fundamentally missing something, as most places I've seen internal resistances for lead acid batteries quoted as under 10 milliohms... normally around 4-6 milliohms

    Certainly, the internal resistance depends on the battery size. Bigger batteries will have smaller resistance. It cannot be one number fits all.
  • mfoobar
    mfoobar Registered Users Posts: 13
    Re: Battery voltage drop question

    Westbranch,
    Thanks for the comments. These are not AGM batteries, just regular wet but sealed ones. Also being a motorhome space on the roof is limited. At the time the 64w panel was the largest I could reasonably fit on there. Now prices have dropped I could get mono panels that take up less space than the unisolar amphorus panel I have. Motorhomes in the UK are a but smaller than the US ;) As I said above the bulk of the charging comes from a 50A DC-DC charger. What I e realised since though is that it is not completing a full charge cycle and the solar panel doesn't have enough power to complete it. Even if it did I would have two separate chargers with no communication between them, so the solar regulator wouldn't know to continue an absorption phase and would just go to float.

    -Matt
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Battery voltage drop question

    Yes with the drop in price you can now 'afford' just about any panel out there.
    If you do do for one of the higher output panels it would be to your advantage to go MPPT so as to make use of the full output of the panel(s), even though the are more costly.
    That amorphous panel's output may be dropping already, so it may not even be worth trying to match it. available space on the roof becomes the limiting factor, though some threads here have talked about tilting panels, especially if you don't move often or far...

    hth
     
    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
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery voltage drop question

    Roughly, you can get almost twice as many Watts / WattHours from crystalline solar panel vs amorphous panels from the same sq foot/meter space.

    However, glass panels are fragile and can be easier to shatter vs plastic thin film panels.

    Otherwise, the glass crystalline panels should last many years longer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Battery voltage drop question
    mfoobar wrote: »
    I've just given it a charge of up to 15.1v for a few hours, which got it bubbling a bit
    mfoobar wrote:
    These are not AGM batteries, just regular wet but sealed ones.

    You might be making things worse... too much bubbling might dry out a sealed battery. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mfoobar
    mfoobar Registered Users Posts: 13
    Re: Battery voltage drop question

    Yes, I'm aware causing sealed batteries to gas too much is not a good thing to do regularly. It's not a process I intend to repeat. It was intended to equalise the cells and try and blast off some sulphate.

    -Matt
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Battery voltage drop question

    "Blasting" off sulfate, is pointless, you need to re-disolve the crystals, not drop them into the sump. The more crystals you have, the weaker the electrolyte is. Dissociating water does not dissolve the crystals, but it will vent precious water to the atmosphere, that you cannot replace.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mfoobar
    mfoobar Registered Users Posts: 13
    Re: Battery voltage drop question

    It may be a moot point anyway. The original replies to my original question seem to think that 12.4 - 12.5v is what they would expect to see on a battery under 4A of load.

    However the graphs then posted by BB seem to show a much higher voltage. If you look at the C/20 line at 100% SoC it shows a voltage of around 12.6v, this is 5.57A on a 110Ah battery, so higher draw than the 4A i was talking about. So I still don't understand what voltage I really should be seeing with that kind of load. And further don't see how that relates to the <10 milliamp values I keep seeing when I see data sheets for batteries online.

    -Matt
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery voltage drop question

    I would not take those graphs as gospel... They are only rough indications of what you might see... Battery construction, initial acid fill, temperature, age, sulfation, how they have been treaded by the owner, etc. all will affect these graphs.

    I am confused about the 10 milliamp specification--How/where is that used?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Battery voltage drop question
    mfoobar wrote: »
    And further don't see how that relates to the <10 milliamp values I keep seeing when I see data sheets for batteries online.

    Battery is a complex electro-chemical system. Voltage drop depends on the speed of electro-chemical reaction, which depends on many other factors. It varies from battery to battery, and even for single battery it is not easily prdictable.

    You cannot reduce the battery to an ideal voltage source and a resistor connected in series. This is too simplistic.
  • mfoobar
    mfoobar Registered Users Posts: 13
    Re: Battery voltage drop question
    BB. wrote: »
    I am confused about the 10 milliamp specification--How/where is that used?

    Sorry, my typo. 10 Milliohms is what I meant. Pretty much all figures I've seen on data sheets for lead acid batteries are under 10 milliohms. The suggestions above of a voltage drop of 0.3 - 0.4V for a 4A load equate to 75 - 100 milliohms internal resistance.

    -Matt
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery voltage drop question

    Lead Acid batteries have very low internal resistance (a good thing for a battery).

    However, it does make placing batteries in parallel (to increase battery bank AH capacity) a bit more difficult. If the wiring resistance difference between strings is significant (i.e., higher resistance than battery bank)--A miss matched set of parallel strings will "steer" current to the battery string with the lowest resistance (heaviest, shortest wiring).

    You can look at the Smart Gauge website for more information on how to wire a parallel battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery voltage drop question

    Bill
    Could you find a simular efficiant battery diagram for correctly wiring 16 batteries in a 48 volt configuration?
    Thanks
    gww
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery voltage drop question

    What is the voltage of the battery (2/4/6/12/24 volts)? I.e., 4 parallel strings, 2 parallel strings, etc...

    Is there a preferred orientation? One long string against the wall, or in a matrix?

    In the end, I am not sure I have any "better" ideas. There are only so many ways to wire up a series/parallel connection setup.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery voltage drop question

    Bill
    6 volt sams club, not bought yet, I don't have a prefferance on set up as I can't visualize how much room they take. I have a bookshelf type dresser but dont know if 16 batts will fit but I am pretty open as long as I can service them.
    Thanks
    gww
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery voltage drop question

    If you have room, I would put the two strings of batteries in a "U" shape. Either on a rack (8 on the bottom and 8 on the top with room in-between for you to service), or 8 to the left and 8 to the right with the Inverter/charge controllers in the middle.

    Either will keep the cabling short. As long as the overall cable length is the same between the two strings--They will have balanced wiring and should have reasonably balanced current flow.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery voltage drop question

    Bill
    + - + - + - with one wire from beginning + and one wire from the ending - with the starting + wire and the ending - wire going to the respective buss bars. Do this twice and make sure the wires that leave the batteries to the buss are all the same lenght.
    Good luck understanding this one. No comunication expert here.
    Thanks
    gww
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery voltage drop question

    Yep--You got it.

    Note that the total overall wiring length should be about the same for each string... If, for example you have 2' on positive cable and 1' on negative for one string, and 1' on positive cable and 2' on negative on the other string--That is fine. It is the total electrical length to keep "balanced" between parallel strings.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery voltage drop question

    Bill
    I don't know how many time this is going to happen but here goes,
    "Thanks"
    gww
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Battery voltage drop question

    4 amp load might be a bit light to observe this somewhat counter intuitive result but you may see the battery voltage drop for the first 1 or 2 minutes then begin to rise again over the next 10 minutes before gradually starting to drop again. Sometimes referred as surface charge burn off I believe it is due to excess lead oxide build up on positive plates if battery has been on float charge for some time.

    I do load tests on my 105 AH batteries, about once a year, with 25 amp load for 30 minutes (about 15 AH discharge), then measure open circuit rested voltage after 30 minute recovery time.

    Start open circuit 12.8 vdc
    apply 25 amp load (almost 0.25 C load)

    1 min 12.0 vdc ( oh my god !, the battery is bad,)
    5 min 12.10 v
    10 min 12.13 v
    15 min 12.15 v
    30 min 12.05

    after 30 min rest with no load rest, back up to 12.75 vdc open terminal voltage
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery voltage drop question

    my way of thinking is that he is severely undercharging those batteries with 1 64w pv that is most likely not optimally aimed most of the time and also has sulfation in the batteries as a result. a charge will show the voltage you would normally expect it to reach, but a subsequent load will pull it far lower in voltage due to the batteries' poor state. these batteries may all be toast and i suggest you get them tested just to be sure before replacing them. more pv is a must for your setup and, as was already mentioned, 5% would be the minimum charge to a battery and 10% as a better goal along with about 13% as a maximum without knowing if the battery can take more. add to that the fact you may not be optimally aimed could warrant an even larger pv, but it's hard to say without knowing exactly how far off your aiming is.

    5% of (115ah x 3) 345ah = 17.25a
    10% of the same 345ah is 34.5a
    13% would be 44.85a

    that's a far cry from the 3.88a max at stc that you are getting from a single us64 pv. if you are going to use a pwm cc then when buying the pvs pay more attention to the imp rating and not so much the watts. an mppt cc will take more advantage of the watts, but cost more even though many of the cheaper high powered pvs may cost considerably less.
  • mfoobar
    mfoobar Registered Users Posts: 13
    Re: Battery voltage drop question

    RCAinFLA,
    Thanks for your data points. That is certainly interesting to see that the voltage comes up a bit for you after a while. I'll try doing my tests for longer and see what happens.

    Niel,
    Indeed... That is what my conclusion is, that they are possibly sulphated due to undercharging. Hence this thread... to try and find out what 'normal' is for a load on these batteries so I can try and ascertain if mine are damaged as a result (and if so how badly). I've learned a lot in the past couple of weeks looking at all of this. I originally didn't think my solar panel was too small (considering it was just for keeping float and providing a bit of extra power to extend my battery run time). But I'm now starting to think that it may even be doing more harm that good, as it has been effectively fooling my B2B charger that that batteries are indeed full when they are not.

    -Matt
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery voltage drop question

    ok matt. well, a battery's rating is indicative of its ability. a 100ah battery is usually at a 20hr rate. this means that 20hrs of 100/20=5a would bring the battery to dead or 0% soc. most rate the dead voltage to be 10.5v, but that is an at rest voltage as the voltage would come back up to 10.5v after many hours of no loads or charges. i don't recommend you doing this as it would put a bigger strain on your batteries that you already suspect are bad than what you could get from a load test. some garages and mechanics have this and may be able to give your batteries a testing without making them dead. i suggest calling around to see if any of your local mechanics can do this for you.
  • mfoobar
    mfoobar Registered Users Posts: 13
    Re: Battery voltage drop question
    RCinFLA wrote: »
    4 amp load might be a bit light to observe this somewhat counter intuitive result but you may see the battery voltage drop for the first 1 or 2 minutes then begin to rise again over the next 10 minutes before gradually starting to drop again. Sometimes referred as surface charge burn off I believe it is due to excess lead oxide build up on positive plates if battery has been on float charge for some time.


    I just found this paper which is quite interesting:

    http://www.smartgauge.co.uk/pdfs/external/battery_modelling.pdf

    It talks about the effect you observe, Coup de Fouet, on page 39.

    -Matt
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Battery voltage drop question
    mfoobar wrote: »
    I just found this paper which is quite interesting:

    http://www.smartgauge.co.uk/pdfs/external/battery_modelling.pdf

    It talks about the effect you observe, Coup de Fouet, on page 39.

    -Matt

    That got me looking and I found this reference which seems quite comprehensive, though shallow.
    http://www.mpoweruk.com/life.htm
    Among other things, it explains that in addition to the lower chance of thermal runaway in an LiFePO4 cell compared to an LiCoO2 cell, the LiFePo4 has an almost zero volume change during charge/discharge cycling compared to the LiCoO2 cell (Boeing 787), and that this repeated mechanical stress can damage the separator leading to a short circuit!
    The fact that the Boeing batteries were unexpectedly being discharged to a lower SOC than planned because of ground operator error may be a critical factor in the reduced cell life.
    SMA SB 3000, old BP panels.