testing the main battery before warranty expiration?

2180 Views 30 Replies 6 Participants Last post by crackers8199, 2 mo ago

crackers8199

Discussion Starter · 2 mo ago

now that we finally have our car back after the fight with GM to get the coolant sensor fixed under warranty, i'm thinking i should probably run a thorough test (or at least as thorough as i can do myself) on the battery to make sure it's not failing - our battery warranty runs out at the end of july. i did take this screenshot of the battery fully charged in MGV, which i think (based on what i've been able to find in my research) looks OK - but we did also have a propulsion power reduced happen immediately after we got the car back from the dealer (on the way home once the battery ran out), so i'm wanting to make sure we're not going to have this thing die on us just after warranty.

what exactly should i do from here? the gist of what i've seen seems to indicate we should do this again (look at the individual cells) both somewhere around the midpoint and then also right before it switches to gas, and also right after it's fully depleted and has sat for a bit unplugged...is that right?

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fhteagle

· #2 · 2 mo ago

Okay so you've checked top balance (looks good to me). Now, start from full like that and in one continuous drive session, preferably on highways without big speed changes that create regen, and definitely no stopping, charging, or engine use, see what the kWh delivered on the Energy page says when it turns itself over to gasoline power. Hopefully you are going a reasonable highway speed on a level road not accelerating at that time, hills or lead footing it can make the engine come on sooner.

Have a passenger take the MGV display screenshot again as soon as possible after the gasoline engine kicks on, to see your "bottom balance" of the pack.

Those three data points are the best info we have at this point on SOH.

There is a MyVoltCapacity app, but I don't really trust it.

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hellsop

· #3 · 2 mo ago

fhteagle said:
Okay so you've checked top balance (looks good to me). Now, start from full like that and in one continuous drive session, preferably on highways without big speed changes that create regen, and definitely no stopping, charging, or engine use, see what the kWh delivered on the Energy page says when it turns itself over to gasoline power. Hopefully you are going a reasonable highway speed on a level road not accelerating at that time, hills or lead footing it can make the engine come on sooner.

Have a passenger take the MGV display screenshot again as soon as possible after the gasoline engine kicks on, to see your "bottom balance" of the pack.

Too complicated. The difference between the "engine turns on" point and the "engine turns off" point is about 2% of available charge, so they're quite close together. Just drive however you need to drive until the engine turns on, and at the next convenient point, pull off, wait until the engine stops, let the cell display go through a complete refresh at least once to get a stable reading, and take your picture. If you have a problem, it will be dramatic enough that the difference between the low- and high-water points of the generator range won't tell you much.

And, if you're thinking you DO have problems already, trying to barrel down the highway to get to the switchover point is exactly the kind of driving that's likely to to "maybe I have a problem" into "I definitely have a problem" because the most likely way to pull a cell into a critically low voltage is by rapidly drawing power out of a low battery to start the engine and then wait 30 seconds for it to warm up to start generating at full capacity.

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crackers8199

Discussion Starter · #4 · 2 mo ago

hellsop said:
Too complicated. The difference between the "engine turns on" point and the "engine turns off" point is about 2% of available charge, so they're quite close together. Just drive however you need to drive until the engine turns on, and at the next convenient point, pull off, wait until the engine stops, let the cell display go through a complete refresh at least once to get a stable reading, and take your picture. If you have a problem, it will be dramatic enough that the difference between the low- and high-water points of the generator range won't tell you much.

And, if you're thinking you DO have problems already, trying to barrel down the highway to get to the switchover point is exactly the kind of driving that's likely to to "maybe I have a problem" into "I definitely have a problem" because the most likely way to pull a cell into a critically low voltage is by rapidly drawing power out of a low battery to start the engine and then wait 30 seconds for it to warm up to start generating at full capacity.

so, highway driving isn't necessary? it can be around town?

and does it all have to be in one shot or can it be a few smaller trips? we don't usually take the volt out aside from short trips to the store and small errands...i honestly don't know the last time it saw an extended period of highway driving (but we do need to get a smog test done this week, so it'll have to be driven around a bit to get the engine to kick on for that, from what i've been told).

hellsop

· #5 · 2 mo ago

Just need to get the battery charge down as far as the car will let it under normal circumstances, then stabilized with only a minimum of change to the demand on the battery for the 10 seconds or so that it takes to get a clean reading. That stability is WAY easier while pulled over while driving and you won't need a passenger to take the screenshot.

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crackers8199

Discussion Starter · #6 · 2 mo ago

perfect. i'll leave my model 3 in the garage today then and use the volt for my daily errands...i should be able to drive enough over the course of the entire day (several small trips) to run the battery out. will report back once i get a low reading.

fhteagle

· #7 · 2 mo ago

The kWh delivered figure gets pretty inaccurate pretty quickly with a lot of stop and go / regen use, any engine use, etc. It wasn't really designed to be a diagnostic tool, but I don't know of much better.

What hellsop said about the reading being more stable at a stop is accurate. I've tried doing it all three ways, passenger getting the screenshot while rolling (with a very very very steady go pedal foot), with coming to a stop after ICE engagement, and with being at a stop and just running the heater until engine on SOC is reached. From my observations, the latter two methods might hide a weaker cell that the first might show. But if the battery is truly has a cell group bad enough to be concerned about, it would probably show up on all three methods. Just depends on how picky you're trying to get.

crackers8199

Discussion Starter · #8 · 2 mo ago

2

here are the MGV pictures both just after the switchover (which happened about a mile from my house, so i pulled over and took a quick screenshot there) and then again after i backed in and parked in my garage, turned the car off, and back on in service mode.

the switchover was just after the display hit 9.2 kwh, and i got 35.9 miles on battery.

first image: just after the switch to gas. i pulled over literally almost exactly as it was switching over.

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second image: after i drove the final mile from where it switched to gas to my house, backed into the garage, and let it sit for a minute before taking this one...

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hellsop

· #9 · 2 mo ago

Hooray! The two reads are pretty consistent, which is good because it increases confidence that they're right. And while not great, they're also not an imminent permanent failure. Section 1 (the one at the front of the longitudinal tunnel under the center armrest that contains the high-numbered cell groups) is definitely weaker than the others, but 40mV isn't a disaster. You MAY want to avoid bumping the bottom of the charge while climbing an entrance ramp to freeway speeds if you can help it, but Mountain Mode (or Hold Mode) before getting on the freeway will probably keep you rolling for a while longer without PPR events. (My 2012 is about the same voltage divergence, and that's the same principle I'm working from: don't let it bounce too hard on the bottom, and it stays looking okay.)

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crackers8199

Discussion Starter · #10 · 2 mo ago

so, basically work from the principle that if we leave the house knowing we are going more than 30 miles or so, just put it in mountain mode from the jump...or if not and we end up out longer than expected, put it in hold with 2-3 bars left instead of letting it run all the way out?

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hellsop

· #11 · 2 mo ago

crackers8199 said:
so, basically work from the principle that if we leave the house knowing we are going more than 30 miles or so, just put it in mountain mode from the jump...or if not and we end up out longer than expected, put it in hold with 2-3 bars left instead of letting it run all the way out?

That's basically how I operate these days. (2012, so no Hold...) If I know I'll run out of charge, Mountain Mode. If I might run out of charge, it's usually because I'm already on city streets, and not taking highway to get home, and I'll just let it go. It's the consumption of electrons between "I'm low enough to turn on the ICE" and the 30 seconds or so it takes for the ICE to warm up a bit then spin up and actually start producing enough power to exceed what driving is using that I worry about problems. That's TRIVIAL amounts of juice at 30 MPH or knowing I'm approaching a stop in a couple blocks, but a respectable/scary amount climbing a hill at 70. If I'm out and my plans change to exceed range by a lot or by freeway miles, it's turn on MM as soon as I know.

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crackers8199

Discussion Starter · #12 · 2 mo ago

hellsop said:
That's basically how I operate these days. (2012, so no Hold...) If I know I'll run out of charge, Mountain Mode. If I might run out of charge, it's usually because I'm already on city streets, and not taking highway to get home, and I'll just let it go. It's the consumption of electrons between "I'm low enough to turn on the ICE" and the 30 seconds or so it takes for the ICE to warm up a bit then spin up and actually start producing enough power to exceed what driving is using that I worry about problems. That's TRIVIAL amounts of juice at 30 MPH or knowing I'm approaching a stop in a couple blocks, but a respectable/scary amount climbing a hill at 70. If I'm out and my plans change to exceed range by a lot or by freeway miles, it's turn on MM as soon as I know.

i really wish there were a way to automatically put it in MM without having to remember to hit the damn button every time we get into the car. for us, even half of the battery range would probably cover 90% of our usage (we take my model 3 pretty much any time we're going further than just to the grocery store or a doctor's appt, or something small like that), so i'd be fine with keeping half the battery in reserve at all times and using a little bit of gas just to make sure i don't kill it permanently.

noyoudont

· #13 · 2 mo ago

there is another variable i will add to this
if you charge your battery at half empty to full your mv will creep up
mine got up to 120mv
i now do full cycles and my mv have reduced back to 12 mv empty
i think gm addressed this with an update, not sure
and as i type this i do realize that on a weak battery when your not tring to empty the battery
this might be a counter productive solution

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crackers8199

Discussion Starter · #14 · 2 mo ago

noyoudont said:
there is another variable i will add to this
if you charge your battery at half empty to full your mv will creep up
mine got up to 120mv
i now do full cycles and my mv have reduced back to 12 mv empty
i think gm addressed this with an update, not sure
and as i type this i do realize that on a weak battery when your not tring to empty the battery
this might be a counter productive solution

this one is harder for me since the car sits in the garage plugged in the overwhelming majority of the time. we'd have to leave it unplugged for weeks at a time to in general be able to get enough usage to empty the battery on a regular basis...we usually just take it out for whatever errands need running, and then plug it back in when we get home. on a normal day it gets less than 15 miles of use, and it only gets used two, MAYBE 3 times a week if that. some weeks not at all. we both work from home, so it just doesn't go anywhere all that often since we take the model 3 on most of our longer trips.

hellsop

· #15 · 2 mo ago

noyoudont said:
there is another variable i will add to this
if you charge your battery at half empty to full your mv will creep up
mine got up to 120mv
i now do full cycles and my mv have reduced back to 12 mv empty
i think gm addressed this with an update, not sure
and as i type this i do realize that on a weak battery when your not tring to empty the battery
this might be a counter productive solution

Can you elaborate on this in any way? Provide examples, or point to someone else that's had the same experience? The only downside I remember to half-charges is the tendency of the car to get pessimistic about how far a charge will wring out and a couple of full cycles will remind it of how much capacity it actually has.

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noyoudont

· #16 · 2 mo ago

hellsop said:
Can you elaborate on this in any way? Provide examples, or point to someone else that's had the same experience? The only downside I remember to half-charges is the tendency of the car to get pessimistic about how far a charge will wring out and a couple of full cycles will remind it of how much capacity it actually has.

a few years back, in one of my alias on this forum i mentioned that my mv was getting up wares of 120 mv, not consistent, but all over the place and was wondering if my battery was going south. i would drive to work, use just over half my battery, plug in at work, charge back up and drive home using just over half again and charge at home. did this for over a couple of years. any other driving we would use the other volt.
some one on this forum, responded to my question, and asked a few question and responded that they did not consider that scenario when you were charging. i just assumed it was a gm engineer that had responded. but that got me to thinking that maybe becouse i was not doing full discharges that it was affecting the battery. so in a hail marry, nothing to lose. i started to do full discharges( not charging at work) that made me use 1.25 litres of gas a day, i know, using gas
took about 4 months and my mv now range from 12 to 18 mv, dont mind using a little gas now, car has over 160,000 km
take it, for what its worth

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wordptom

· #17 · 2 mo ago

noyoudont said:
a few years back, in one of my alias on this forum i mentioned that my mv was getting up wares of 120 mv, not consistent, but all over the place and was wondering if my battery was going south. i would drive to work, use just over half my battery, plug in at work, charge back up and drive home using just over half again and charge at home. did this for over a couple of years. any other driving we would use the other volt.
some one on this forum, responded to my question, and asked a few question and responded that they did not consider that scenario when you were charging. i just assumed it was a gm engineer that had responded. but that got me to thinking that maybe becouse i was not doing full discharges that it was affecting the battery. so in a hail marry, nothing to lose. i started to do full discharges( not charging at work) that made me use 1.25 litres of gas a day, i know, using gas
took about 4 months and my mv now range from 12 to 18 mv, dont mind using a little gas now, car has over 160,000 km
take it, for what its worth

Here’s a thought that just occurred to me... perhaps when you fully charge, then don’t deplete it much, then recharge, the relatively minor drop in average cell voltage before recharging doesn’t result in a large low/high cell differential, and isn’t enough to trigger a cell balancing procedure upon recharge (perhaps that’s what the engineer meant by saying they had not considered that scenario). So when you fully recharge, any small cell group voltage difference from that discharge cycle isn’t corrected. Each subsequent short drive followed by recharging without cell balancing eventually widens the difference for those weaker cell groups. Perhaps once you do drain the charge further before recharging, this then triggers a cell balancing episode, and the system eventually corrects the imbalance (and perhaps GM corrected this issue with their Cell Balancing Update)???

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noyoudont

· #18 · 2 mo ago (Edited)

wordptom said:
Here’s a thought that just occurred to me... perhaps when you fully charge, then don’t deplete it much, then recharge, the relatively minor drop in average cell voltage before recharging doesn’t result in a large low/high cell differential, and isn’t enough to trigger a cell balancing procedure upon recharge (perhaps that’s what the engineer meant by saying they had not considered that scenario). So when you fully recharge, any small cell group voltage difference from that discharge cycle isn’t corrected. Each subsequent short drive followed by recharging without cell balancing eventually widens the difference for those weaker cell groups. Perhaps once you do drain the charge further before recharging, this then triggers a cell balancing episode, and the system eventually corrects the imbalance (and perhaps GM corrected this issue with their Cell Balancing Update)???

kind of what i thought after it corrected itself, and it wasnt the update that fixed it, i only did the update at 150,000 km, just before the warranty ran out on the battery. it had returned to 12mv long before i did the update
checked my differential this morning, 12mv
my thought at the time,was that there wasnt enough time/voltage drop in the cells to do a proper balance when you half charge

crackers8199

Discussion Starter · #19 · 2 mo ago

I think the overall key is that we're going to have to start getting the car out of the garage a little more often in general. it's just rough though since the model 3 is a better car...hard to justify driving the volt when I can use autopilot on the highway in the Tesla.

hellsop

· #20 · 2 mo ago

Sounds like you're basically at a "use it or sell it" stage, and selling it might not be a bad idea. You don't seem to actually need it.

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