Oliver Jobson

The right way to charge Car Batteries – EFB, AGM etc – CTEK MXS 5.0 or Noco

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Modern batteries and modern smart chargers: From basic charging to reconditioning, stratification and sulphation

During the Covid pandemic car battery chargers became far more important. And they continue to be for many people who aren’t using their car anywhere near as much as they used to. However, with the proliferation of different battery technologies, start/stop and hybrid battery systems that we now have, do you know the correct way to charge your car to maximise the life of the battery and prevent damage?

I have posted a number of questions to CTEK customer support over the last couple of years in regards to using my the MXS 5.0* on different battery types. Partly, this is because info on the web is lacking, or sometimes incorrect (many car forums carry inaccurate info), but the user guide is also light on info. So I compiled this guide from their responses (and some extra advice from other sources) as a personal reference and to help others. Whilst it is written primarily for the CTEK MXS range of car battery chargers, much of the information will still be relevant for most other types of charger.

*Most of the modern smart chargers, including the Noco range, are broadly similar in functionality and use)

In this article:

In car charging

So – from what CTEK support tell me – you can connect your CTEK MXS charger to the battery while it is installed in the car. Even the RECOND programme mode, where the max voltage peak is 15.7v (+0.3v higher than non-RECOND programmes), SHOULD be perfectly safe for MOST cars. Typically, anything under 16 volts shouldn’t cause any problems for a modern car. Having said all that, there are bound to be exceptions. It is definitely worth taking the time to check this with your car manual or manufacturer – as getting it wrong could be costly). A short safety guide is also available here.

The CTEK MXS 5.0 charger is robust and suits a number of different use-cases; charging large and small batteries, and many different types. They are well rated and CTEK offer lots of different models.

But what about other brands of car charger?
Read: Guide to charging with a Noco Genius5

Flooded (Wet) and Enhanced Flooded Batteries (EFB)

Typically for Flooded and Enhanced Flooded Batteries you would just use the mode button to select the car icon and charge with this mode. Standard flooded or “wet” batteries, which are more prone to stratification and sulphation, may require use of the RECOND programme periodically.

EFB batteries contain technologies and designs to destratify the battery acid (electrolyte), as well as being able to be cycled more deeply without detrimental health impacts like sulphation occurring (Read: What is an EFB battery?). This means you are less likely to need to use the RECOND mode, or see the charger attempt desulphation – read on about that below…

RECOND Programme mode

First off, only use RECOND mode with a standard Lead Acid Battery or Enhanced Flooded Battery (EFB) (this includes calcium EFB batteries). RECOND will not help an Advanced Glass Matt (AGM) battery. It could even harm a Gel battery. Find out more about what RECOND mode does in the Stratification section below. RECOND + AGM programme can be safely used on Ca-Ca (Calcium or Silver Calcium) type batteries, see more below.

Desulphation (Charging stage one)

Desulphation happens automatically, if required – not just in RECOND mode. Every CTEK charger mode starts with a desulphation step at the beginning. If the charger diagnoses a sulphated battery, it will attempt desulphation. If not, it will move on to step two.

Sulphation is where sulphuric acid crystals build up inside the battery on the electrodes. This typically happens when a battery spends periods of time in a partially charged or uncharged state. During desulphation the charger will pulse voltage peaks to help break down and remove these crystals.

CTEK chargers will spend as long as is required, or until a prefixed period of time has lapsed, on desulphation. To give you an idea, this is usually a number of hours, not minutes. If the charger is unable to complete this step within the time period it will show an error and the charger will not move on to the next step. You may need to attempt this process several times if sulphation is extreme. I have had success with small 7Ah AGM UPS batteries in the past, but never with a dead car battery. If after several attempts you still receive an error then you may need to replace the battery.

Stratification

What the RECOND programme includes is a process called destratification, which creates a controlled gassing that remixes the acid and equalises the acid balance. This process helps to reclaim battery capacity and restore battery efficiency. The success of the reconditioning process depends on how severe the problem is.

What Stratification physically is is a situation where the electrolyte, which is denser, sinks towards the bottom of the battery cells and thereby ‘starves’ the top of each cell, thereby reducing the voltage potential of the battery and its cold cranking power.

Stratification can happen if the alternator charging voltage is too low or the charging time is insufficient (due to short drives, or heavy use of accessories that reduce charging current), or where a battery is deeply discharged and unused for a period. Different batteries suffer more or less from stratification, depending of the battery type and design.

Because AGM or Gel batteries do not suffer with stratification, RECOND mode won’t help revive these types of battery. It may even damage the health of Gel batteries – more on this here in my Guide to car battery technologies.

AGM battery charging with the AGM mode

The AGM programme uses a slightly higher voltage (+0.3v) at it’s peak. That’s all. It will still attempt a desulphation stage at the start of the programme if deemed necessary by the charger. The higher voltage is just better suited to these types of batteries. (Read: What is a AGM battery?)

Calcium battery charging

The reason for the CTEK charger AGM+RECOND mode:

So if destratification doesn’t benefit an AGM battery, why does a CTEK charger provide an AGM + RECOND mode? The answer is that Calcium batteries can benefit from this programme. Calcium (Ca-Ca) batteries (More info here) can suffer from stratification, so using RECOND to create a gentle gassing in the battery can help restore power (See: Destratification, above). As calcium batteries typically charge at higher voltages, they are better suited to the AGM programme mode and its higher voltage (+0.3v). Hence it being possible to use the AGM and RECOND programmes together.

Check out the CTEK charger on amazon >

Thanks to CTEK customer support for answering my many questions!

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Comments

33 responses to “The right way to charge Car Batteries – EFB, AGM etc – CTEK MXS 5.0 or Noco”

  1. Juinn avatar
    Juinn

    Hi Oliver,
    Through the power of google I found your page about the CTEK charger which I also have. (CTEK 5.0). I have been charging my car battery over night and have a bluetooth sensor that sends the voltage status to my phone but also logs the voltage. Would you be interested in screenshots of the battery voltage graph? It may give some insight into what the CTEK does during certain modes.
    Kind regards,
    Juinn

  2. Oliver Jobson avatar
    Oliver Jobson

    Yes! That would be good to see. I’ll ping you an email.

  3. Joel Smith avatar
    Joel Smith

    This is an excellent write up. I found info on charging EFB units quite limited when first using the CTEK charger so a guide like this would have helped a lot.

  4. Oliver Jobson avatar
    Oliver Jobson

    Thanks for your comment. I also struggled to find info on how to charge EFB batteries (for my previous car), so that was one of the reasons I wrote this post – I’m glad you think it’s helpful.

  5. David avatar
    David

    Hi
    Just bought the 5.0 model for our Evoque as getting start engine low battery messages and specialist advised this as due to Covid lockdown the car isn’t getting enough long runs although in last month have done a couple
    I selected modes for car and AGM which the battery is
    Goggling found a reply from CTEK technical which said the RECOND mode won’t help or harm the battery
    The charger has now got to setting 4 having been on about an hour
    The car display says Low battery start engine which I don’t fancy doing. Don’t know why it says this as car not started but bonnet is up
    So will the charger display setting 5 then 6 etc and will that take a few hours?
    Thanks Oliver

  6. Oliver Jobson avatar
    Oliver Jobson

    Yes – wait for the charger to finish all the steps and if the charger detects a fault it will show a warning lamp. Otherwise if all is ok the green light at step 7 will be displayed and then it will go in to maintenance / trickle charge mode to keep the battery topped up. We’ve had to do this to both our cars over the last couple of weeks. It could take a few hours to get to step 7.
    Once done you can then disconnect the charger and it should start fine. In terms of the low battery message – it might take a short run or two for the car diagnostics to assess the battery as being ok and then remove the warning message. If it persists then you might need a technician to reset the code and/or do further investigation into either the battery of the battery charging system.

  7. John C. avatar
    John C.

    Hello:
    I have a question about the CTEK MXS 5.0 settings. The battery on my BMW R1200RT motorcycle is a gel type. What would be the appropriate mode setting for this? Should I use the motorcycle/agm or just the motorcycle alone setting? Neither the manual nor the FAQs cover this. Thank you.

  8. Oliver Jobson avatar
    Oliver Jobson

    On page 4 of my manual it says that the standard battery charging program can be used for gel batteries. From what little I know about gel batteries the charging current must be less that 14.5v – the standard CTEK programme will be no more than 14.4v and should therefore not result in a dried out battery.

    If your battery is less than 14ah then you can use the small battery program (motorcycle icon). If it’s more than 14ah (the R1200rt is a big bike but not sure how big the battery would be) then you need to use the standard battery charging program (with the car icon).

  9. Frank M avatar
    Frank M

    Hi Oliver, what an incredibly useful blog post, thanks for sharing. I have been worried about using my XS 0.8 on an EFB battery since I noticed yesterday on the CTEK website no mention of EFB compatibility with any CTEK charger bar the CT5 Start/stop charger. I sent an email to CTEK earlier today about this very subject. I now need to figure out if the automatic door opening buttons on my Seat Alhambra are flashing because I didn’t disconnect the earth lead from the battery while I’ve been charging it and why my battery won’t hold any charge despite my battery tester telling me the battery needs recharging which I’ve been trying to do for the last week! Thanks again.

  10. Oliver Jobson avatar
    Oliver Jobson

    I’ve never had a problem with charging whilst the battery is connected – I would suggest that electrical issues would be due to the battery needing charging. See if the issue persists once you solve your battery issue.
    With EFB batteries my experience has always been that they work great until they are dead and then need replacing (usually at around 6 or 7 years old). But then, those cars never sat still for long periods in a lockdown. How old is the car / battery?
    A clean of the battery terminals might also help, but I would venture two possible hypotheses: you need a higher wattage charger (like the mxs 5.0), or the battery is dead and needs replacing.

  11. Frank M avatar
    Frank M

    Thanks for your reply. As far as I can tell from the paperwork received as part of the purchase the battery is the original, car is a 2013 Alhambra. I was convinced the battery was the issue til I tested it, tester may be dodgy tho but is brand new. Either way, you’re right about the need for an upgraded charger, it’s on my list. Thanks again.

  12. tony avatar
    tony

    Hi Oliver, my battery is EFB type but my car has start stop technology. Do I still use standard mode setting as opposed to AGM please?

  13. Oliver Jobson avatar
    Oliver Jobson

    Charge the battery in normal mode for an EFB. Might also be worth asking if your car is supposed to have an EFB battery in it. Could be why you have run in to problems?

  14. Mike avatar
    Mike

    Hi Oliver, thank you so much for sharing this great info & knowledge, in the CTEK MXS 5.0 manual it says “AGM option – use for charging most AGM batteries like Optima and Odyssey”, does that mean some AGM batteries should not use this AGM mode?

  15. Oliver Jobson avatar
    Oliver Jobson

    Well that’s a really good question. I’ve not encountered any issues in charging OEM AGM batteries so far. The only variation I can find mention of online for AGM batteries is where some manufacturers (including Odyssey) market “Thin Plate Pure Lead” (TPPL) technology. However, other manufacturers claim that this is more of a gimmick: (https://www.trojanbattery.com/pdf/Facts-About-TPPL-Technology.pdf). That document does make mention of poor quality Chinese batteries … so perhaps when CTEK say “most AGM batteries”it is more a matter of varying quality being an issue, rather than it being about variation of AGM technologies. Could be worth posing that question to CTEK tech support!

  16. Alan Taylor avatar
    Alan Taylor

    I just wanted to say thanks for this very informative article and for covering EFB which I feel really should be mentioned in my MXS 5.0 manual. (May 2022)

  17. Martyn pope avatar
    Martyn pope

    Great post, I have recently started to experience low battery message and also slow to cool air con (not sure if linked to battery) I charged the AGM over night with my CTEK MSX 5.0 on AGM recond, it finished without any errors but my car still displays low voltage warning and the air con issue. Could the battery still be failing even if the ctek said it was fine ? Thanks

  18. Oliver Jobson avatar
    Oliver Jobson

    Sometimes the car needs to have the battery management system reset.
    Might need to have a garage to do this unless you have an OBDII diagnostic tool and software. Sometimes if you leave the car with the battery out for 8 or 12 hours it will do it for you.

    What does the battery voltage read first thing in the morning? Ideally it needs to be higher than 12.2 volts.

    The other test is to have someone read the battery voltage with a multimeter whilst you start the car – if it drops below 10.5 volts then it is likely shot.

  19. Nmgcle avatar
    Nmgcle

    Thank you so much for this very useful information that Ctek itself fails to provide. I am a happy owner of the MSX 5.0 and I think the purchase is probably the best money I’ve ever spent. I drive my car rarely and only on short trips, especially in our very cold Winter months, and was previously plagued by finding that my car would not start and that my batteries needed replacement much too soon. This little device has been a godsend and two years in it continues to function flawlessly. Now, I can always approach my vehicle with confidence, knowing that the battery will always start. I have a two year old AGM battery and couldn’t figure out when I should be using “recondition mode”. Thanks to you, I now know that’s unnecessary and not something I need to worry about. The device itself is super simple to use and is basically plug and play, but the manufacturer really needs to provide more information related to the product. Thanks very much for so intelligently filling in the blanks!

  20. Dean avatar
    Dean

    Hi Oliver, thanks for the info.
    I just purchased a 100Ah LIFEPO4.
    Can I use my MXS5 to charge or will the Desulphation start up or other stages mess with the BMS.
    Thanks for your time.
    Dean.

  21. Oliver Jobson avatar
    Oliver Jobson

    In short – No, this is not compatible.
    Lithium batteries require a more advanced battery management system, which the MXS 5.0 is not designed for. You need something like the CTEK Lithium XS

  22. Dean avatar
    Dean

    Thanks Oliver.

  23. Ryan Tack avatar
    Ryan Tack

    Hi Oliver, I have a 2019 2.0 Corolla hybrid with the 12v battery in the boot. From what I can find out it’s a standard 12v not a AGM? It says in the manual the positive must be disconnected before charging but I was hoping that with the MXS I wouldn’t need to do this and fit the fast connector from my previous car?

  24. Oliver Jobson avatar
    Oliver Jobson

    If it specifically mentions not to do this, then I would be very careful to against the hand book / user manual.
    I would seek advice from CTEK themselves and/or an automotive electrician, or a dealership.
    Toyota may be giving this advice because some chargers can deliver high currents / voltages or voltage spikes that may damage sensitive electronics – so they are protecting themselves and their customers with this general advice.
    The advice I got from CTEK customer support was that their chargers are specifically designed to not do this, and should be safe on most cars.

  25. John avatar
    John

    Does connecting a battery charger (Ctec 5.0) into the mains before connecting to the battery do any harm

  26. Oliver Jobson avatar
    Oliver Jobson

    Doing so would go against the directions in the user manual. I can only hypothesise that it could cause voltage spikes that may damage any sensitive electronics.

  27. Dave avatar
    Dave

    A very interesting and informative blog Oliver. I’ve been looking all week for info and found very little.
    I recently bought an 18 month old Ford Kuga diesel which is fitted with a Varta EFB+C battery. A lovely car, but it monitors everything, so needs lots of power. It never fails to start, but shows low battery most of the time (driving very little). So, thinks I, charge required, like in the old days! After charging over night with my trusty old Banner smart charger, it was only slightly better. My charger peeks at 14.4v. I investigated on Varta web site and found EFB’s need 14.6-14.8v to charge. I believe 14.8v not to be exceeded!
    So reading your paragraph “In car charging” and seeing you state 15.7v is safe (with caution) and even 16v ??? I was filled with constanation!
    Would be interested to hear your views on this point.
    Regards.
    Dave.

  28. Oliver Jobson avatar
    Oliver Jobson

    I do say that: 1) this is “typically” ok, and 2) that this info is what I have received from CTEK customer support, and 3) that it is worth checking in your car manual.
    But I have made the wording a little clearer to inform readers that there is still risk here.

  29. Colin D'Avila avatar
    Colin D’Avila

    It seems to me that battery manufacturers are keeping useful information about batteries hidden. One example of this is Battery State of Charge vs Battery Voltage for the different battery technology’s. You can find old tables that give this information for AGM, VRLA, Ykon and Wet batteries but nothing for the EFB batteries. If people know the state of charge voltage for their batteries, they can maintain them better

  30. Oliver Jobson avatar
    Oliver Jobson

    I agree! Very difficult to find this kind of information and so hard to know how “full” a battery is. Modern battery design (to provide, as close as is possible, a constant voltage) makes it a increasingly difficult to get a decent idea of how full a battery is via simple measures – like measuring voltage.

  31. Ben avatar
    Ben

    Hi I have been reading lots which contradicts itself with regard to AGM. To clarify… I have just bought a CTEK 5.0, I have also just bought an Exide 30ah AGM ready sealed maint free gel motorcycle battery (however to be used on a kit car). I assume from reading this I need to charge using the car setting, not AGM? Thanks Ben

  32. Oliver Jobson avatar
    Oliver Jobson

    From what you have told me, you would use the Car and AGM settings. I’ll add a disclaimer that it’s always sensible to check with CTEK and/or the manufacturer of your bike. The car / bike setting is to do with the size of the battery. The AGM setting is for the battery type.

  33. Jim Aston avatar
    Jim Aston

    Thank you for your article. Cleared up my confusion as I, like probably many thought that all stop/start cars used AGM batteries. Not helped by car manuals not listing type and battery manufacturers descriptions the same. Now realise AGM’s are marked as such by no such identification of EFB type.
    Bought a CTEK 5.0 after having the battery changed under warranty but still getting the car closing down systems to conserve the battery (very short journeys now) automatically used AGM setting. As you say CTEK not clear on this matter.

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