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Electron Summit White NK13...107k 91.5 and rising
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Discussion Starter · #1 ·
I've not seen much discussion on this but I think my HV battery may be beginning its decline. I first noticed it a couple of months ago but put it down to the cold weather and kidded myself that things would return to normal. Up until then I wa getting 10.1 - 10.5 KWh out of a full battery. Now it is in the range 9.6 - 10.1. I rarely get 5Kwh out before the GOM battery indicator drops below the halfway mark. Looking at the Octopus Agile graph, there is definitely about 1Kwh less going in on a charge. Interestingly, adopting @donald's use of Mountain Mode on longer motorway journeys can push this up to 11KWh, but apart from that I seem to have a 5% battery degradation. Car is now 8 yrs old with 107k miles on clock. Lifetime mpg is 91.5.

I've not noticed any other effect. On a hot day I can get 44-45 miles out of a charge and its quite hilly around here, so I have no reason to complain. But I'm unlikely to make the 50 mile club I think.

My next step is to download one of the enhanced OBD apps to look at the cell voltage spread.

Does anyone know if there is anywhere independent in the UK that is able to strip and rebuild the battery packs? I was thinking of perhaps getting one out of a wreck and then replacing weak cells. I know there are companies in the US that offer that service.
 

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Electron Summit White NK13...107k 91.5 and rising
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Discussion Starter · #3 ·
You could try a local HEVRA garage if there is one near to you.
Actually, there is one in Yeovil. I wasn't sure if the HEVRA tag indicated that level of ambition. It's a thought.
 

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I've not seen much discussion on this but I think my HV battery may be beginning its decline. I first noticed it a couple of months ago but put it down to the cold weather and kidded myself that things would return to normal. Up until then I wa getting 10.1 - 10.5 KWh out of a full battery. Now it is in the range 9.6 - 10.1. I rarely get 5Kwh out before the GOM battery indicator drops below the halfway mark. Looking at the Octopus Agile graph, there is definitely about 1Kwh less going in on a charge. Interestingly, adopting @donald's use of Mountain Mode on longer motorway journeys can push this up to 11KWh, but apart from that I seem to have a 5% battery degradation. Car is now 8 yrs old with 107k miles on clock. Lifetime mpg is 91.5.

I've not noticed any other effect. On a hot day I can get 44-45 miles out of a charge and its quite hilly around here, so I have no reason to complain. But I'm unlikely to make the 50 mile club I think.

My next step is to download one of the enhanced OBD apps to look at the cell voltage spread.

Does anyone know if there is anywhere independent in the UK that is able to strip and rebuild the battery packs? I was thinking of perhaps getting one out of a wreck and then replacing weak cells. I know there are companies in the US that offer that service.
I use My Green Volt app on an android phone to check the battery cell voltages. You have to buy the full app (for less than £2) to read the cell voltages. Most bluetooth OBD scanners work OK. I use ELM 327 from eBay similar to this.
I know you can change battery modules but I have not seen anyone able to replace individual cells.
 

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Electron Summit White NK13...107k 91.5 and rising
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166 Posts
Discussion Starter · #6 ·
Thanks for the helpful suggestions. It's booked into Robert Cockings in Yeovil on 2nd July for them to take a look, upon which experience I will report back. I've also ordered a bluetooth ELM327 and will take a look at MGV. Seems I will have to actually spend money on an app for once. I did have a WiFi OBDII dongle but had quite a lot of trouble getting it to work reliably.
 

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Electron Summit White NK13...107k 91.5 and rising
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Discussion Starter · #7 ·
This gets weirder. Tonight I posted my membership of the 40 Club. Yesterday I used about 6kWh and decided not to re-charge overnight. When I got in the car this evening, the GOM battery was higher and the available range had gone up. I thought it only did cell balancing at the top and bottom of the charge cycle. Anyway end result was 44.5 miles (which is not that unusual) - but also10.4kWH. I know its only a guess and stochastic and statistical as @donald says, but I've not seen anything like that since March.

146008
 

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Warm battery overnight? Or did someone sneak round and feed the gremlins...
 

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The BMS does updates whilst monitoring the battery, it is quite common (for Ampera) for the reading to change a few .1 kWh. Usually during temperature changes, both ambient and battery temp (after fast drives).

Remember what I keep saying;- it is impossible to 'read' a battery's state of charge, a battery is more 'cooking recipe' than 'precision engineering'.
 

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This is highly unlikely to be degredation. Sparky has done 477k miles and has 12% degredation and still putting out 10.4kwh due to the buffer.
 

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Electron Summit White NK13...107k 91.5 and rising
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Discussion Starter · #11 ·
Things are improving. I got 47.5 miles today from 10.2KwH today. Still not the 10.5 I was getting last year, but at least its consistently over 10 now. I've been reading a lot of posts on similar apparent loss of capacity on the GM-Volt forum (not the one induced by the reprogramming update). There seems to be a consensus there that frequent partial charging without regular complete top to bottom cycling can produce the effect, but the good news is that it is not necessarily permanent. When I first noticed the drop I had been doing a lot of partial charges. Also, they say leaving the battery at min SOC for a while to allow cell balancing to complete helps, rather than charging immediately after a run.

I'm thinking of cancelling the HEVRA visit for now.
 

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Electron Summit White NK13...107k 91.5 and rising
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166 Posts
Discussion Starter · #12 ·
Just to wrap this up, I called the helpful people at the HEVRA garage in Yeovil (Robert Cockings 01935 349105) and after discussing the apparent recovery decided to defer any investigation until/if a more tangible problem arises.
 

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Electron Summit White NK13...107k 91.5 and rising
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Discussion Starter · #13 ·
Bit of an update on this after having had the opportunity to go through a few charge cycles now and pay attention to details. Even thought the usable battery capacity now appears to be more or less the same as last year - about 10.3KwH - I've noticed that capacity can only be achieved if I discharge the battery in two roughly equal stages, with an overnight rest in between. If I discharge it in one go, I always get high nines or 10 if I'm lucky. That is different to last summer when it would regularly give 10.4/5 in a single run. So something is happening to the chemistry.
 
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