Battery Charge Maintenance for Garage Queen

[EricUSC]

I recently acquired a very early Roadster 1.5. The battery was replaced in January 2014 (3 years ago) due to bricking. The car has been driven ~3,000 miles since the new battery was installed and has a full standard mode range of 182 ideal miles. The Roadster is not my daily driver and will be driven every 2-4 weeks. I plan to get OVMS so I can have greater control over setting the state of charge (SOC), but I'm waiting for the 3.0 version of OVMS to become available.

QUESTIONS:
1. Is it better to maintain charge in Storage Mode or Standard Mode when the car is stored between drives?
2. I thought I read somewhere that OVMS allows the vehicle to maintain a state of charge (like 50-60%). Is this a better strategy and if so, what SOC should I maintain the battery at when the car is stored between drives?
3. Please share your charge strategy if your Roadster use is similar to mine.

Thanks!

 

[snd92]

Ideally you should finish standard charge and leave it for 30-60 minutes for balancing before driving. After the drive don't let it fall below 50 % SOC. That is what I do and I drive mine 1-2 times a week, sometimes 1-2 times a month.

Driven 36 000 km, CAC = 152-156 Ah (291-298 km on standard charge), original battery

 

[Mark77a]

Contrary to many folk on here, and even guru @dpeilow I now leave mine plugged in 24/7 standard charge ie ~80% SOC (not range or storage). Sometimes it's a daily driver, sometimes its a garage queen (depending on weather in UK and trip schedules)

The reasons:
1. I tried various recommendations (most folk say 60% is ideal long term SOC for longevity .. it probably is, but the pack is a bank of cells and so I believe balance is more important - say you go for a drive from 60% average SOC and 1 or 2 cells are lower SOC due to greater self discharge/variations... when 'pulling amps' (as you do ) these cells get pulled down to a lower voltage and even lower SOC.. this is THE worst treatment for a cell.
2. I found my CAC goes up gradually when used and kept plugged in . (OK very slight - cf long term gradual aging)
3. I found my CAC goes down when using keep 60% > charge > drive scenarios.
4. (probably THE most compelling) ... I know several people in Tesla UK who have not only worked on Roadsters since day 1, mix with original Roadster battery development team. These people ALL recommend and DO plug in their own roadsters 24/7 standard mode (cars include low mileage future classics / low VIN numbers as well as daily drivers)

FWIW I'm on original battery 7 years old now, 31000 miles with a current average CAC of 144 (172 ideal miles)
(Subjective averages: 1st 4 years was plugged in 24/7, CAC was 155 to 150, years 5&6 using more kept at 60%> charge > drive, CAC 150>140, year 7 24/7 standard charge ie ~80% SOC, CAC 140 > 145)

 

[Roadster]

I recently acquired a very early Roadster 1.5.

Do tell: EP, VP, Founders, Sig?

 

[EricUSC]

Do tell: EP, VP, Founders, Sig?

Founders'

 

[gregd]

Ok, 24/7 plugged in Standard mode is the best strategy. Next question: What charging current?

The "Jeff Dahn approach" might be to limit the time at elevated temps, so higher current (40 amps) should be better. Pump it in, cool it down, done and over with as quick as possible. Alternatively, if the car is only driven a few miles a week (trips to the grocery store) as mine is, perhaps a lower current (24 amps?) would accomplish the same by limiting the heating aspect of the charging cycle, since the battery wouldn't actually get that warm during driving or charging.

For what it's worth, I seem to get a couple of miles higher standard charge at the lower current, though that might just enable the charger to better estimate the actual charge at the lower rate (to not overshoot the target). My 2010 2.0 is currently at 44.4k miles, and a standard mode charge around 165 miles. CAC just dropped from 140.2 to 139.3 last week.

Thoughts?

 

[hcsharp]

The reasons:
1. I tried various recommendations (most folk say 60% is ideal long term SOC for longevity .. it probably is, but the pack is a bank of cells and so I believe balance is more important - say you go for a drive from 60% average SOC and 1 or 2 cells are lower SOC due to greater self discharge/variations... when 'pulling amps' (as you do ) these cells get pulled down to a lower voltage and even lower SOC.. this is THE worst treatment for a cell.

Well said! When your pack is stored at a higher SOC it produces less internal heat when driving. Not only is balance more important as you elegantly stated, but a cooler pack is also more important.

Smaller charges more often are also better than larger charges less often. For example, charging from 40% to 80% is harder on your battery than charging twice from 60% to 80%. The result is less impact for the same number of miles driven. The anode has a certain amount of physical instability that gets stressed more with deeper discharges, causing more breakdown, or microcracking of the Li compound.

 

[Tesla 940]

I'm not going to dispute what any of the experts have said because they certainly know more than I ever will ... but... FWIW, my car is 7+ years old, 30k miles and while I have NOT abused my battery, I have in no way "babied" it. After a HARD 3 days of racing in June at Laguna Seca my range charge was only 205 ideal miles. After 5 range charges my max is now 226 ideal miles - that is 92% of original capacity. When I leave town for weeks up to 10 weeks at a time, I leave the car at ~70% charged and set for "storage" just in case.