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Thread: battery is at 12.5 volt when "charged"

  1. #21
    Raw Wave
    Join Date
    Nov 2009
    I'm not a qualified mechanic but I once worked as a mechanics labourer; I have often corrected qualified mechanics' knowledge and some specialised mechanics are bewildered at some of the details I know; and I have always done my own car & bike repairs and work including and engine rebuilds (excluding actual reboring, regrinds, brake & clutch relines & skimming).

    But this is not the domain of mechanics - in fact some still think the alternator's output goes thru the voltage regulator or that the regulator should be set to 13.8V!
    It may be the domain of auto electricians, but batteries are usually the domain of the battery industry.
    Even then, like mechanics, there are some woozy practitioners - like the battery supplier of 20 years that reckoned that "sealed batteries - AGM and gel - are all the same".

    My battery origins come from the technology pushers which filtered down to commercial products like automotive & solar and battery suppliers.
    Since then it has been one of application and problem solving and keeping in touch or meeting new commercial types - eg, knowledgeable and experienced battery suppliers for the auto industry. Though battery technology changes (eg, safe LiPo & lithium technology), that has little relevance to most vehicles which are predominantly still lead-acid, and most principles are transferable anyhow (ie, their circuit model is the same). Advances like calcium are a minor step change (eg to voltages).
    IMO the biggest change I have seen was the shift from the "all correct" constant-current charging for AGMs in the 1990s to their now accepted and universal constant voltage charging which (thankfully) made them compatible with wet & gel cell batteries. [That's a separate issue to current limiting, but that is not a consideration in most vehicles. And those that push "priority charging" obviously have even less regard for current limiting (LOL).]
    Last edited by OldSpark; 06-22-2013 at 05:32 AM.

  2. #22
    Variable Bitrate
    Join Date
    May 2010
    Herákleion, Iraklion, Greece, Greece
    well, i didin't asked to see if what you guys say , is correct.. i asked because you BOTH do exactly what a mechanic does. you make an extremely big deal, about something that really is a pice of crap! i dont mean isolators( wicch indeed are a great deal, solenoid or diode) but for batteries. ? Altarnators dont break down because of the batteries. Alternators break because they are from japan, and they suck ***.none of the cars i have been around (family or friends cars (many many cars) ) have ever had a bad alternator, and believe me , some of their batteries, are even 8 years old, and dont even support the lighting! every post i have ever seen related to power problems, you guys just go inside and swarm the **** out of it, about batteries in parallel or how to isolate them, without even giving the slightest input on how to solve the actual problem (telling someone to buy something is not help. ITS WHAT A MECHANIC DOES. if i wanted something bought, i wouldn't even need to be a part of a forum. i would just pay someone to do all the **** for me. )

    AS FOR THE SAME OR NOT BATTERIES. god its so simple! every battery has an internal resistance. the internal resistance is a factor of its maker AND the history of the battery. that is what makes it different from another battery (at same amps).
    if you connect to batteries in parallel, without any isolation, and they are different, its battery will see the other as a resistance and they will both get discharged after (allot) of time.
    if there is an isolation, the loeads on every battery will be different anyway, hence CHANGING THE HISTORY, so even if you buy to same batteries, and the one runs the car, and the other the 8bilion watt sound sytem, after one year THEY WILL NOT BE THE SAME BATTARIES ANYWAY.

  3. #23
    Raw Wave
    Join Date
    Nov 2009
    LOL! I don't have the problems that redheadedrod or others keep mentioning BECAUSE I use Jap alternators (but the Japs are regarded as masters of such electrical things). Like you, I have driven on 7V batteries.
    It wasn't until I tried Bosch alternators (German) that I experienced such problems. And recently I found that others had similar experiences with certain GM alternators.

    And yes, you are totally correct about one battery supplying in other. But that is NOT what I have been discussing. I have only been discussing batteries connected together whilst they are being charged and hence one battery cannot discharge into - or charge - another battery.
    I have only been discussing the application of battery isolators which are fitted for just that reason - to charge both batteries whilst keeping them isolated and independent when the engine if off or not charging.
    If you think that that is complicated, then the discussion regarding paralleling to supply loads will blow your mind. That involves current paths (intercabling) which is not relevant for isolators, plus all the other factors such as resistance and SOC that you mentioned which - as I have said time and time again - are not relevant to battery isolators wrt the context that I have discussed them.
    And not that internal resistance has much to do with anything. That varies with SOC and temperature and has no effect on how they should be connected or charged. Battery capacity and SOC are the critical parameters (plus temperature...).
    But I am glad that you see something that Red seems to have missed - ie, your last paragraph.

    But you have had your problem(s) answered. And more than once. Hence I didn't think the hijack was that bad. But if you do, who was it that interjected?

    Next time I'll ask you one or a few questions at a time rather than give you a universally applicable reply. I dislike that sort of iteration, but if relevant information is not provided...
    Else, where I can, I'll simply answer the question. No value add. No caveats or traps or suggestions.

    If you don't think you have your answer but want me to start again (using the simple & direct approach), just say so.

    Or I can delete my replies if you prefer. (Tell me which ones you want kept if any.)

  4. #24
    Variable Bitrate
    Join Date
    May 2010
    Herákleion, Iraklion, Greece, Greece
    no dude. i find your posts extremely informative, and you do good give that much info. BUT i believe that they luck of a direct DIY approach (which if you try to give, might be lost inside the details? )

  5. #25
    Raw Wave
    Join Date
    Nov 2009
    Thanks. And I know what you mean. I am often told to KIS (Keep It Simple) and I did do that for a while in forums. But I've slipped back into my old "one document for all" tech type writing which was typically read several times by readers, though it was better segmented and ordered and usually more a case of one section at a time.

    So are you clear about your batteries? IE - that one is almost certainly dead, and the other one certainly damaged.

    Whether either can be rejuvenated depends on whether they are AGM (they'll be stuffed), or new and not have been at a voltage less than (say) 12.3V for too long.

    As to how this has occurred, are you using a diode isolator, or a relay isolator, else what else?

    Sorry - that is more than one question at a time, but it covers the 3 main areas I consider relevant.

  6. #26
    Maximum Bitrate
    Join Date
    May 2012
    Grandville, MI
    I was professionally trained to work with car electronics systems with relations to car audio and security systems. I held a professional level certification and have had training in electrical and technician training.

    I don't have to prove anything to you old spark. We have gone around and around about this and you won't listen to reason. So since there is a difference of opinion the user should go to an RV shop that does this sort of thing every day. Not a car audio shop that wants to sell you something expensive or a dealer that will charge you an arm and leg.

    Old spark you didn't even want to believe there was such a thing as a diode isolator or a dual output alternator until I showed you. I have also showed you sites you can research the correct information but you try to find loop holes to make your story sound like the right one when it goes against the science behind it. I am not going to waste my time. The best thing I can do is tell the member to check out what we tell them at a reputable RV dealer.

    As to testing your batteries or alternator.. You can not detect a cell being bad or a diode being burnt out. When an auto parts store runs it on their machine they can tell right away. I have had batteries that tested fine with the testing old spark tries to show but it doesn't work 100% of the time and requires extra equipment people don't always have. Taking them to an auto parts store is free. If you have a single diode go bad it will test fine in your car, won't throw a code or show anything is wrong but still won't charge your battery. The tester at the parts store WILL show a single blown diode. I have had a single diode blow in an alternator more than once and test fine in the car until you take it to a place that can test them and the diode pack is bad.

  7. #27
    Raw Wave
    Join Date
    Nov 2009
    Come now Red, enough of this crap.
    I think your giveaway was...
    Quote Originally Posted by redheadedrod View Post
    If you have a rechargable battery charger would you charge a C & D cell together in a paired battery charger? Or even charge two different brands in the same paired channel?
    I reckon just about anyone knows how false that is.

    Professionally trained? So are you qualified?

    I was writing about diode isolators before you even joined this site. Dual output alternators - what is their relevance here?

    I already commented on some of your sources. Please - by all means - start a new thread and repeat those same sources and post the relevant parts. I will blow them away for the same reasons they were irrelevant last time. But keep in mind, we are talking about parallel batteries WHEN CHARGING - not jump starting etc etc.
    I think you misunderstand them the same as you misunderstand me, or twist them as you twist my writing - eg, about testing a battery is 100% ok whatever. (I haven't even mentioned capacity testing in this thread, only voltage testing for SOC and OC voltages. And I'm sure I have mentioned on mp3car that the problem with battery capacity testing is that it makes no guarantee that the battery will have that capacity next time - even if within weeks. Battery testing technology has been a high priority for well over 20 years and yet they still haven't nailed it - even for our ancient and "mature" wet lead acids.)

    A blown or shorted alternator diode can not be tested in circuit? Do you really lack such expertise? Oh hang on, you say a shop can. I'm confused - so it can be tested. What you are saying is that vehicles do not have the required circuitry etc? I thought you were saying it could not be tested.
    So who tested your alternator? I found a shorted diode using my DMM. That's simple. In another cases I have correctly diagnosed open diodes and that must have been with a DMM because it was way before I got a cheap CRO (which I never use anyhow LOL).

    As to collapsed cells I agree, but with a fully charged new battery that is only 10V or 8V it is reasonably certain it's 1 or 2 collapsed cells. But I gave the example that a (say) ~10.5V fully charged OC battery could be one collapsed cell or several faulty cells. Big deal - it's a stuffed battery - end of story.

    And I have never disagreed about getting anything professionally tested. If it's free, why not.
    But for those that want to test themselves for whatever reason I provide alternative methods. Those with eyes but no DMM can do certain charging system tests. Those with a DMM can do much more.
    I think you confuse my buyer - or rather - testee beware with "don't go to a free tester". I merely provide extra info to try to prevent readers paying unnecessarily for what may be a simple blown fuse of bad connection and not a faulty alternator or battery. Good pros won't charge for that, but some will take advantage (and some don't know better). Some battery fitters don't even check the alternator output voltage after fitting a new battery!
    Otherwise the answer to settra's problem IMO is simple - take your system and batteries to a tester. End of thread.

    If you think the science is wrong, state where and how. Are you saying 2 parallel components or batteries do not have the same voltage? Or are you referring to me contradicting the sources I have given and others like, Wiki, etc or other hardtexts?

    Albeit privy to our PMs, I have offered to discuss your claims with your professional teachers. So now for all to see, I repeat the offer. Provide me with contact details and I'll take it from there. Even a phone number since verbal realtime is the quickest & least complex communication means for things like this.

    If you seek alternate support for your claims, maybe try as that specialises in car security and audio. Though some may not have good expertise in vehicle power supply systems (some reckon any 2 batteries can be paralleled when NOT being charged - I'm not sure if I successfully educated them otherwise) and some make the odd incredulous claim, I think you'd find little support. I also contribute to There are many other forums, but I am not joining any more public forums. (I am continuing with the ones I am with until I have an external reason to leave.)

    Now please stop harassing me. I still think you are merely stirring, but this extent of provocation IMO is contrary to the rules of this site and general etiquette.
    If you have comments, stick to one issue at a time within the confines of the original statement. That's good - it clarifies ambiguities and misunderstandings, or educates.
    But mere generalised statements are useless, as are statements that can be shown to be false from other reputable sources.
    Opinions are an other issue, but that's one reason I give "general related" replies hoping that readers can balance the varying aspects and decide for themselves.
    And I really don't want to have to go into all the basics and considerations just to clarify or argue some point. It's bad enough that I provide general rolled up info, but for OPs I may be prepared to do it.

    So please, rational discussion. Stop bloating settra's thread.

    settra - again, apologies.
    And again, if you want me to stop...
    As of now I shall ignore all future replies by redheadedrod in this thread and only comment if you so ask.

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