Battery Health Check procedure - correct method?

[ThudnBlundr]

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.

Except that it's charging for way, way more than half the time when the ICE is powering the car on a long journey...

 

[greendwarf]

So still less than all EV - but how do the short charge/recharge cycles count toward the lifetime limit, anyway?

 

[ThudnBlundr]

If each charge cycle while driving normally is (say) 5%, for Lithium batteries you generally count that as 1/20 of a charge cycle. So 20 of them would equal a full one.

But I have no idea how much a charge cycle while driving is, as it's complicated by the fact that the battery has top (and probably bottom) buffers, so even charging to "full" isn't a complete cycle, compounded by the fact that "empty" is really 30%...

 

[greendwarf]

And does this change significantly once in parallel mode, when there seems to be very little energy left over to charge the battery? - typically on long motorway trips at high speed.

What surveys have found is that many company car users (who wanted the car for the tax break) rarely plugged the car in to charge - basically just driving an ICE car. So I still think it is reasonable to suggest that this sort of usage will have "degraded" the battery less than one used almost exclusively in EV mode - at the same road mileage.

 

[Mo1820]

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.

<span>I bought an <a href="http://www.amazon.co.uk/gp/product/B005NLQAHS/?tag=myelecarfor-21&" interlinkr"="" target="_blank">OBD2</a> 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.</span>

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.

Hugwi and all, sorry I didn’t see this until now. I managed to get a battery health check done last Monday for the car I want to buy - yes it did take some persuading and time! Pse see attached pics of Worksheets 1 and 2 that I was sent, which might help people on here.

Worksheet 1 says that the 'current capacity' of the battery/BMU is 37.8/37.7 Ah/amp - which seems to be good if the capacity for a new battery is 40? Since it looks like the ‘Requirement’ question, no. 3, says 'What is capacity for a new battery?’ being 40. Hence I assume 37.7 out of 40 is good? Although if this is the case I’m confused as to why the technician has written ’40' by hand - ie. why isn’t this figure already pre-printed if it is a standard figure to be compared to? Also not sure why he’s highlighted the 40 as opposed to the 37.8, as I thought it was the 'current capacity' I’m meant to be concerned with?

If anyone can inform me as to what all the other numbers mean I’d be grateful - eg. I think (but am not sure) that the cell voltages handwritten in the table under point no. 2.1 mean that the battery is in good health? Or under question no.s 4.1 and 4.2 what is the implication of testing the battery with the fan at 32 rpm and what does the ‘duty control %’ mean? If it is run at 10%?

According to another Mitsu dealer any amp reading above 25.6 means the battery is healthy. If this is the case it means the car I’ve just had tested has a healthy battery? Which implies yours is also good at 31.2 Ah - so why do you think it is bad please? As I’m hoping I haven’t misunderstood the info or been misinformed - especially as I’m hoping that all the readings mean the battery is good, so I should go ahead and buy the car.

 

[davep118]

Hi Mo1820,

I'm a newbie to the forum and also to the PHEV so take what I say in the next paragraph with a pinch of salt. According to Mitsubishi Motors (UK), a 16MY PHEV battery capacity when new is rated at 38Ah. So the warranty guarantee of 70% in the first 8 years / 100,000 miles means the State of Health (SoH) of this battery has to fall below 38 x 0.7 = 26.6Ah. Only the newer models (possibly with the 13.4kWh battery) are rated at 40Ah.

The battery management unit comes with an inbuilt Cycle degradation as well as a Time degradation. Therefore, to have only lost 0.2-0.3Ah capacity in the 4-5 years since the battery was first installed would seem to be too good to be true. So I would conclude that either the car has had a new battery (unlikely) or someone has done a reset.

 

[Mo1820]

Thanks DaveP118,

We have bought the car since my last post so hope the battery is a good one. As well as your findings I was also curious to know what all the other figures on the worksheets meant - apart from the Ah ones. When you say someone may have done a reset do you mean of the ECU or BMU?

We think the battery is good because according to the Cheshire Mitsubishi dealer it came into them to be looked at on 12th January, when they said it showed a range of 26 miles - which is good for winter as far as I know. I'd asked for the battery to be checked but also the car had to have a new ECU fitted, as apparently the original one had been corrupted which they think was caused by an error made during a pre-heating app recall. The new ECU was fitted at the end of January and then the battery was tested a day or so after. So do you mean the reset or a new ECU would incorrectly show the battery as 'new'? If so the battery was still showing good range (26 miles) before the new ECU was installed.

We collected the car from Cheshire and drove it to London at the end of February - at the start of the journey it showed 22 miles at 11 degrees outside - I had pressed the 'Charge' button for a short while on the motorway to see if this worked - so by the end of the journey it showed 27 miles at 8 degrees. (Bytheway I had no clue how to use the paddle shift on the steering wheel to increase the battery charge and still haven't read up on how to do this yet - my next post was going to ask for advice on this).

I charged the car between 10.30pm and 4am last week using our normal 13 amp socket, after which it read 33 miles at 6 degrees. So am hoping and praying these are not 'false' readings and that the battery is good. (Grimace emoji?) As the car's manufacturer's warranty period has now expired (end of March) I hope I won't need to ever claim on the 8 year battery warranty.

 

[mellobob]

The displayed range is a guess at best. It's all dependent on what temp of the battery is, use of climate control, what kind of driving you do, terrain, traffic, speed, etc. The car's computer generates this value based on past driving ... the meter is called a "guess-o-meter" ... lots of links on the web about that.

 

[greendwarf]

The displayed range is a guess at best. It's all dependent on what temp of the battery is, use of climate control, what kind of driving you do, terrain, traffic, speed, etc. The car's computer generates this value based on past driving ... the meter is called a "guess-o-meter" ... lots of links of the web about that.

Including this one https://www.electrifying.com/blog/knowledge-hub/10-charging-facts-that-every-electric-car-owner-should-know