Roadster Owner Based Study of Battery Pack Capacity Over Time

[benji4]

Your description of rarely if ever doing a range mode charge makes me think that this might be your problem. If it is, you can just do what I did. Be patient, though. While batteries that aren't terribly unbalanced can get to balance in an hour or so, you may take MUCH longer.

This looks like it's getting a bit off topic, but the above discussion has made me curious about a couple of things:

1) It's apparent that rarely or never charging in range mode leads to imbalances in the battery pack, but can this in itself cause damage or permanatly decrease range? What if the situation is left uncorrected for months or longer?

2) In order to get the batteries to rebalance, why is driving the car down to a low state of charge before charging in range mode neccessary? Wouldn't charging in range mode from any level of charge accomplish the same thing?

[richkae]

I think we are talking about 2 completely different animals and range mode charging solves them both for you.

The first is balancing the battery. Charging in range mode may not require any deep cycle to do this.

The second is knowing the capacity of your pack. If the pack is only exercised between 85% and 70% it loses track of what the full range is.
Charging in range mode from a low SOC to "full" SOC helps it to relearn this.

You may have both issues or only one of them.

[hcsharp]

...
1) It's apparent that rarely or never charging in range mode leads to imbalances in the battery pack, but can this in itself cause damage or permanatly decrease range? What if the situation is left uncorrected for months or longer?
...

It's possible but it wouldn't be much damage. Just like frequent charging in range mode shortens life, frequent deep discharge also shortens life. If your pack is out of balance then some of the cells will be deep discharged much more easily because they are starting at a lower SOC than the rest of the pack. Because those cells are stressed more than the others, they will eventually fail earlier, shortening range and the life of the pack. So a range-mode charge every couple of months or whenever you suspect there might be balance issues is advisable.

While range mode full charge and sitting provides the best balancing, the latest software does some balancing with only a std mode chrg.

[benji4]

It's possible but it wouldn't be much damage. Just like frequent charging in range mode shortens life, frequent deep discharge also shortens life. If your pack is out of balance then some of the cells will be deep discharged much more easily because they are starting at a lower SOC than the rest of the pack. Because those cells are stressed more than the others, they will eventually fail earlier, shortening range and the life of the pack. So a range-mode charge every couple of months or whenever you suspect there might be balance issues is advisable.

While range mode full charge and sitting provides the best balancing, the latest software does some balancing with only a std mode chrg.

That makes sense... so basically while it's 'better' to keep the battery pack balanced, since using range mode charging to correct an out-of-balance battery pack in itself is damaging to the battery pack, it's a tough call. Kind of like chemotherapy for the battery pack.

Then the second problem -- using deep charge cycles to get the range indication more accurate. That really should not be done all that often one would think unless the indication is pretty far off base.

[user497]

Last night I fully charged the car in standard mode and only got back to 164 miles. (When I charged in range mode last weekend I got 208 miles). So it doesn't look like charging in range mode really did anything for me. Unfortunately I wasn't able to fully charge in standard mode in one night so it was recharged over 2 nights (Friday and Saturday). I will try to get the car under 100 ideal miles and fully recharge in range mode to give it another shot. I am bringing the car in for its yearly service in March so I will have Tesla take yet another look then if I don't see more mileage by then.

[benji4]

Last night I fully charged the car in standard mode and only got back to 164 miles. (When I charged in range mode last weekend I got 208 miles). So it doesn't look like charging in range mode really did anything for me. Unfortunately I wasn't able to fully charge in standard mode in one night so it was recharged over 2 nights (Friday and Saturday). I will try to get the car under 100 ideal miles and fully recharge in range mode to give it another shot. I am bringing the car in for its yearly service in March so I will have Tesla take yet another look then if I don't see more mileage by then.

In my case I was down to 179 ideal miles for a standard charge after 6 months and 4000 miles on the odometer. One deep charge cycle followed by a range mode charge got it back up to 185 or 186 on a standard charge at 110V/15A. I may try this again and see if it improves it further. When the car was new I was getting 193+ with standard charging so still a bit off that, but not too bad. Tesla just checked the battery for me last week and said their were no problems with it and the range was still what they considered to be normal. I'm curious to hear what they say about yours as 164 definately seems too low.

[vfx]

Charge rate may have an effect here. Tesla told me that continually charging on my 120V 16 amp plug was getting my battery out of balance. The also noted my voltage dropped down to 100 on occasion and was not too happy about it's effect in the sheets.

I now have a 220V 30A option

[richkae]

shameless bump

[zack]

I had something interesting happen Saturday. I've left the car in storage mode for the last few months and took it out for a 30 mile drive. It started with a range reading of 101 miles, and ended at a range of 103 miles with an ideal range of 142.

[dhrivnak]

I had something interesting happen Saturday. I've left the car in storage mode for the last few months and took it out for a 30 mile drive. It started with a range reading of 101 miles, and ended at a range of 103 miles with an ideal range of 142.

That is entirely possible. The normal range is calculated based on the average usage of the last 30 miles. If you got onto it hard say 25 to 30 miles ago and then took it for an easy 5 miles then you average watts/mile could drop substantially and thus boost your range.