Battery Health Check procedure - correct method?

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Mo1820

Member
Joined
Nov 10, 2020
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19
Am v. confused - your experience would be much appreciated - I have spoken to several Mitsubishi Dealers (MD’s) in the UK but all have different responses. Please can someone inform me correctly?
I wanted a battery health check done on a 2016 GX4hs before purchase from a car supermarket dealer (SD). Car has full MD service history and 41k miles on clock. I also asked if the MD could take a look at the MMCS computer to resolve why the SD couldn’t turn off a pre-heating timer/remote climate control for all 7 days if needed. I posted this in a different thread so as not to over-complicate this one, under 'MMCS error? Pre-heating timer/Remote Climate Control.'

The SD agreed to take it to the MD to check the MMCS pre-heating timer and get an EV/drive battery health check (as opposed to a 12v battery health check). (In November the battery mileage range said 21 miles after a full charge, then after sitting on forecourt for a further month it said 11 miles, then after the SD drove it around a bit last week it said 17 miles, in low December temperatures in Cheshire.) I realise that the battery range will depend on driving habits of the previous driver/journey(s) as well as what else is switched on at the time and the outside air temperature.

However different main dealers appear to use different methods for the BMU (battery management unit?) health check, so I am confused. Eg.:-
MD ‘G’ said their diagnostic machine would do a full battery health check on the EV battery, under the boot, which only takes 30 mins and costs £54. They also said they do a health check on the 12V battery, under the bonnet, which also costs £54 but takes overnight to do as it’s set on trickle charge and they send the information to Mitsubishi HQ but only if they find a fault with the 12V battery.
However MDs ‘C’, ‘W’, ‘P’ plus Mitsubishi HQ said that in order to do an EV battery health check, its test data should be sent to HQ first, before draining the battery (cells?) then slowly refilling overnight, followed by the new data being sent to HQ the next day for comparison and analysis. Then after analysing the data, HQ contacts the dealer with any diagnoses or advice on what to do, if anything.
Of the above dealers, MD ‘C’ charges £114 to do their overnight battery health test, MD ‘W’ charges £98 and MD ‘P’ charges £0 as they said the test falls under the manufacturer’s warranty, not due to expire until March this year.

So there seems to be a lot of inconsistency between different MD’s battery health check methods and costs? Does the EV only take 30 mins to check if it’s good, like MD ‘G’; or does it take overnight/24+ hours, like MD’s ‘C/W/P’?

MD ‘P’ - the free of £ charge dealer - said from doing overnight TSRs (technical support requests) with HQ using before and after data, they rarely see battery health problems. They said if the result (is it the SOH - state of health?) is above 25.6 amp it means the battery is ok.

Another MD ‘H’ said they don’t do the BMU/EV health check on request at all, as they said any battery faults would be flagged up by warning lights on the dashboard. So they said if there are no warning lights then there’s nothing wrong with the car/battery and that the mileage range is only affected/estimated by the last 5 mins of your previous journey.

Please could anyone advise which is the correct test method to check that the EV battery is good? The 30 min one using the dealer’s own 'diagnostic machine’, or the one that takes overnight/24+ hours using before and after data sent off to HQ? - To help me know which of the Mitsubishi dealers can be relied upon.
Can any harm be done/problems arise if either the MMCS or EV battery are ‘reset’, or drained and refilled?
Also should we be given an SOH print out explaining the battery health results and how do I interpret these please? I just want to know the battery is healthy and if driven properly it will provide the expected mileage range for its age/usage.
Will a battery health check be able to help determine whether any past damage or leaks have been caused by rough driving/accidental damage, or from using rapid chargers/CHAdeMO too much?

Also is MD ‘G’ correct in saying that the 12V/under bonnet battery takes overnight on trickle charge in order to assess it - if ever needed? How often would this 12V need testing, or would it only be necessary if the car kept getting a flat battery?

Many thanks in advance.
 
Before our pre-BREXIT friends jump in with their "I wouldn't buy an EV without a battery check" :lol: The problem is UK dealers generally don't want to do this - as you have found out. However, I think the overnight test is likely to be more comprehensive.

But, I have some sympathy with the dealers over this - would you ask for a fuel consumption test for an ICE? :roll:

If you really are worried about range then ask for an extended test drive as see how far you can travel - which, at the end of the day, is all that matters. :idea:
 
Many thanks GD. :) We are in London and the car is in Cheshire, so I'm trying to head off any potential problems before payment and collection as it's so far to return the car if anything goes wrong. (FYI the only other car I've found in the same year, mileage, spec and colour I want is 1k dearer in Surrey).

The SD will let us test drive within 100 miles, or for 2 weeks - whichever comes first. We obviously can't stay overnight these Covid days, let alone two weeks and ideally the only driving we want to be doing, after coming to collect the car by train, would be the drive back to London upon collection (obvs more than the 100 miles permitted).

However I suppose we could do 'an extended test drive' whilst we are in Cheshire? By that do you mean for say 10 miles, or how far do you mean? Sorry I am such a novice!
 
I forgot to add - in November another MD service dept. told me that the way to get the average mileage range would be to fully charge the car by plugging in using normal charge at 13 amp mains. Then drive the car around to decrease the battery/range. Then repeat this - full charge and driving around - for 5 more times/days.

They said that this would then give me the average mileage range expected for the car as the 5 journeys would have reset the computer/battery to my driving habits, to change from the previous owner's habits?
 
It isn't called a guessometer for nothing, I've had mine for over 3 years and have seen anything between 14 and 42 miles on it. If it's low it will drop more slowly and if high very quickly. When it showed 42 miles it dropped 2 miles just getting off the drive, no I don't live in a mansion the drive is 5 yards long. It usually shows 23 miles in summer and 21 miles in winter and that's roughly what I get without using heating or AC. Hope this is of use to you.
 
Thanks a lot Outlander660. It does help to know what readings other people are getting in summer and winter, even if your car sounds a bit younger than this one.
 
There's a lot of rubbish quoted to you by the main dealers. Checking the 12V battery, which is in the boot, is a 2-minute job once they've removed the trim to access it. There is no 12V battery under the bonnet, merely a fuse box with a connection to be used when jump starting the car. The EV battery is mounted underneath the car between the wheels. Checking it properly is an overnight job; you can read the SOH stored in the BMU quite easily, but there's no guarantee that the figure is close to reality on newer cars. That's why the full diagnostic is required

The battery warranty is 8 years on any UK car registered after mid-2015; the warranty for the remainder of the car is 5 years.
 
Welcome to the world of Mitsubishi dealers where very few of them know what the hell they are talking about.

Honestly, I would say that a battery problem is so unlikely as to not be worth thinking about. If it really does turn out to be a dud, which you will find out after some months of use, then there is an 8 year warranty on it as said. Probably at 8 years old, most of them are going to be very close to the threshold of replacement anyway. I would buy on the condition of the rest of the car, paintwork, tyres, equipment spec etc and not worry about the battery or you will go round and round in circles confuse yourself and any dealers and sellers and get caught in paralysis by analysis.
 
To answer question about how far is an "extended test drive"? No need to do anything more than the distance of a full charge if all you are doing is checking the battery. People seem to get unnecessarily hung up about battery condition and predicted range. The only relevant issue is how far will it actually go at 30 mph on a full charge? So in winter on a second hand car it would be unlikely to be more than 25 miles - about an hour of normal urban driving - at the best of times, before the ICE cuts in. No need for overnight stay!

But frankly, unless you live in NW London (in which case you have a service only dealer in Hendon) for 1k difference, I'd be going for the one in Surrey, in case you have an post-sale issues, anyway.
 
Thanks very much everyone - it’s quite reassuring to see that I shouldn’t get too hung up on the battery range reading / guessometer!

Littlescrote - your term paralysis by analysis is a great bang on description!
I really hope the battery isn’t going to need replacing after 8 years though as I’d like to keep the car for longer than another 3 (it’s reg is March ‘16).
I thought the battery warranty was 8 years or 100k miles - so I’m hoping that as the car has done 41k miles it might be ok beyond the 8 years - we’re only occasional users in Zone 2 London with the odd long trip so estimated annual use is only about 3k miles.

Yes ThudnBlundr I read an older thread posted ‘somewhere’ on this forum about SOH readings but frustratingly I can’t seem to relocate it - it also mentioned the reluctance of dealers to test on request.
I recall it mentioned certain good or bad figures/amps? If anyone knows the thread I mean please feel free to direct me?

As I said in my original question, one dealer mentioned the BMU reading should be above 25.6 amp to be considered ‘good’. Out of interest I’d like to know if this is correct info?
It’d be nice to be able to rely on at least one thing a dealer has said. (Sigh!)

He said that he would check that amp figure ‘before’ he sent it to Mitsubushi HQ and before he drained and refilled the battery, sending them the ‘after’ figures for comparison. He said he wouldn’t do the whole battery draining overnight diagnostic if the reading was above 25.6 amp as it would already be deemed healthy(?)

Mitsubishi HQ also said they’d need to be sent the figures for a diagnostic check to be valid.

A couple of dealers did tell me they’d only ever done one or two 12+ hour diagnostic checks ‘on request’ which rarely showed to be bad batteries. They seem to have more likely done overnight health checks for something specifically wrong.

Subject to availability I will also consider the Surrey car - especially if the MMCS glitch/heating timer (separate post) on the Cheshire one can’t be rectified!
 
I'm afraid all these either/or warranties are - whichever comes first. So you've only got until next March for a 2016 car, irrespective of the mileage.

My 2014 car with a similar mileage to the ones you are looking at only had a 5 year battery warranty but I am still getting about 22 miles actual range. Like you, I am in Zone 2 with only occasional out of London trips (plus annual holiday to France) - hence about 7k per year. We are the ideal users for a plug-in hybrid.

One thing you should know, is that lithium batteries have a fixed life based on the number of full discharge/recharge cycles - around 2000. This is presumably where the warranty comes from i.e. 250 per year, about 1 a day. If you have less than this - say 2/3 times a week, they will last much longer, twice a day of more e,g. as a taxi and battery life will be much shorter. With a second hand car, you won't know how many cycles have been used so far - unless this is stored in MMC, which I don't have in my Gx3h (OTHER READERS PLEASE ADVISE) - but a high mileage would suggest fewer charges, due to longer journeys.

However, capacity will tail off over time - so less mileage. What Mitsu have done is introduce a buffer of 20% when new which can't be used under normal circumstances. It appears the software is designed to eat into this over time to "disguise" the decline in capacity. I suppose a full battery check readout would show how much of this reserve is left but you would probably need technical knowledge to understand the figures.

A couple of other points - the current Congestion Charge exemption (£10 per year fee to renew) is due to be removed in October this year, and currently for Westminster Council area only parking on street is almost free . You have to pay for the first 10 mins (so they know when you parked) to get up to 4 hours free parking. NB. In practice you can renew by text remotely and pay for another 10 mins to extend for another 4 hours extra time (i.e. less than £2 per day :p )
 
The warranty for the battery and EV components for a 2016 car (and indeed a late 2015 car) is 8 years, so you have until 2024 to claim for battery degradation. The mechanical warranty is 5 years for those cars.

I've not seen any definitive reference to this extra 20% which the car then uses. Please could you list your source. It seems strange that degradation appears to be fairly linear despite this extra buffer. Are you saying that the BMU still degrades the battery in a linear fashion, but less than it would otherwise as it's eating into this extra 20%?
 
greendwarf said:
I'm afraid all these either/or warranties are - whichever comes first. So you've only got until next March for a 2016 car, irrespective of the mileage.

My 2014 car with a similar mileage to the ones you are looking at only had a 5 year battery warranty but I am still getting about 22 miles actual range. Like you, I am in Zone 2 with only occasional out of London trips (plus annual holiday to France) - hence about 7k per year. We are the ideal users for a plug-in hybrid.

One thing you should know, is that lithium batteries have a fixed life based on the number of full discharge/recharge cycles - around 2000. This is presumably where the warranty comes from i.e. 250 per year, about 1 a day. If you have less than this - say 2/3 times a week, they will last much longer, twice a day of more e,g. as a taxi and battery life will be much shorter. With a second hand car, you won't know how many cycles have been used so far - unless this is stored in MMC, which I don't have in my Gx3h (OTHER READERS PLEASE ADVISE) - but a high mileage would suggest fewer charges, due to longer journeys.

However, capacity will tail off over time - so less mileage. What Mitsu have done is introduce a buffer of 20% when new which can't be used under normal circumstances. It appears the software is designed to eat into this over time to "disguise" the decline in capacity. I suppose a full battery check readout would show how much of this reserve is left but you would probably need technical knowledge to understand the figures.

A couple of other points - the current Congestion Charge exemption (£10 per year fee to renew) is due to be removed in October this year, and currently for Westminster Council area only parking on street is almost free . You have to pay for the first 10 mins (so they know when you parked) to get up to 4 hours free parking. NB. In practice you can renew by text remotely and pay for another 10 mins to extend for another 4 hours extra time (i.e. less than £2 per day :p )

GD I’ve heard different definitions about the 5yr/8yr warranties. Where I thought you had 5 years for the car and 8 years for the battery a Mitsubishi HQ customer service advisor (called Ariel) recently told me that only the ‘capacity’ of the battery warranty was claimable for 8 years if it dropped below 70% within that time. Which he said meant that if the car was outside of its 5 year warranty then the rest of the battery wasn’t claimable for the remaining 3 years - just the ‘capacity’ holding part?

If he is correct it sounds like it’d still be expensive to rectify if the capacity dropped lower than 70%, despite having an ‘8 year warranty’?

Good to know that if I charge the battery less often it should last longer. Unfortunately I don’t know whether the previous owner/s ‘rapid’ charged it a lot - from what I’ve read this degrades the battery - so I hope they didn’t. Yes it’d be great if the computer actually displays this info?

Will the battery also hold it’s charge/mileage range if the car is not used for a week or so? (Due to lockdown etc.) Will it also maintain its capacity or will this drop without regular use?

I knew about the congestion charge no longer being free to EV/PHEV users from Oct this year but I didn’t know about the almost free parking in Westminster, thanks GD. I’m obviously wanting a PHEV due to the ULEZ anyway.
 
Lithium batteries degrade with use due to charging/discharging. They degrade over time regardless of use. They will happily hold their charge for weeks, though storing a battery with high or low charge also degrades the battery. For long-term storage, it should be around 50% full as this is close to the equilibrium point for the internal chemical reaction.

There is no proof that rapid charging degrades the battery, merely unproven conjecture. And don't forget that in normal driving the car charges the battery way more than 50% of the time once it shows empty (or you press Charge or Save).

Basically using the car degrades the battery; not using it degrades the battery. :roll:
 
I don't disagree with ThudnBlundr but we went into the battery technology in great detail in the early years of this forum (not sure if threads are still available) so I am relying my amateur understanding and what aged memory can recall. :roll:

As I remember, whilst it may be lithium batteries do degrade over time anyway, it was shown that the ultimate limiting factor is charging cycles, as I described. No doubt individual usage, including too frequent rapid charging, may have some effect on this, but it would appear to be only marginal.

In the last 7 years there have only be a handful of suspected battery failures and only a couple of warranty replacements, in the early days, that I remember - i.e. manufacturing faults, which would have already surfaced in a second hand car and dealt with.

No, I haven't seen any "proof" about the BMU using the buffer with age but this was suggested as a reason why Mitsu have the buffer at all, rather than offer a longer range when new. One of our departed Aussie contributors did experiments with trying to run the batteries flat by deliberately running out of petrol. As I recall even though showing "No Charge" the car went back into EV mode once the ICE died but he still didn't get to exhaust the batteries - he only got a few miles in Turtle mode down to about 10% capacity.

So unless there is some technical reason that has not been explained here why there is a buffer other than as a reserve to maintain a useable range, why is it there? Of course, very few drivers who measure capacity would have needed it yet (given their relative newness) - so most of us may be using the buffer but don't realise. :idea:
 
Batteries degrade more as they near their theoretical capacity, so I wonder if having a buffer at the "top end" would reduce degradation. Most EV manufacturers appear to do this, though it appears that Tesla do not. That would mean that the buffer would remain as the battery degrades, which appears to be borne out in practice. Obviously I don't know either, but this explanation seems to fit the typical degradation pattern.

Not sure if there's anything "at the bottom" as the PHEV tries to maintain significant charge even when showing empty
 
Due to the milder weather yesterday 11 degree C this morning my PodPoint APP recording 9.9kWh for a full charge, normally this time of year due to the colder weather we normally see 9.6kWh.
 
I am in a very similar situation to the OP having just purchased a September 2017 4hs from a car supermarket and I have been getting really variable range readings (from 9 to 30 miles) after a full charge off a 13a home socket.

I bought an OBD2 dongle and with the free version of the phev watchdog app can see that the battery has a SOC of 77% and 31.2aH - I'm slightly surprised that it's so low and the car has only done 32k miles.

I was considering taking it into my local dealer and seeing what they could do under the warranty (I have read several reports of people managing to get their local dealers to do the battery cell smoothing procedure under warranty) but am sure I will just be fobbed off.
 
Battery degradation is not linked to mileage but the number of recharges, with a lifetime limit of around 2000 full cycles. So a car only used in EV for most of its life will show a greater decline than one used for mainly lengthy journeys powered by the ICE.

However, I would not judge battery effectiveness by what the guessometer shows - especially when it gives the wide variety you report. This is more likely to be a function of the different types of journeys you have undertaken e.g. lengthy downhill stretches under EV power (i.e. coasting) can produce ridiculously high range forecasts, if done just before charging - similarly, living at the top of a hill will demand a lot of energy to lift 2 tonnes in altitude whilst only travelling a short distance horizontally. :idea:
 
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