topping off battery several times a day

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jev77

Active member
Joined
May 2, 2010
Messages
36
I have been keeping a driving log for about a month and it appears that I drive anywhere from 70 to 100 miles almost every day. Since I am retired I do not have a commute every day so my typical driving day is, as an example: 20 miles then home for 4 hours, 35 miles then home for 2 hours, 37 miles then home for the night. My question is: Does plugging in and topping off 2 or 3 times a day shorten battery life? Thanks
 
I was involved with some lithium ion battery management software back in the 1990s.

With all battery technologies, you get a finite number of recharges before the batteries die. I have absolutely no idea how many times you can recharge the batteries on a Nissan LEAF before they get to the stage where they cannot take another recharge, but I have talked to some lithium battery manufacturers about EV batteries and depending on the configuration somewhere between 6,000 full recharges and 17,500 full recharges - depending on the battery chemistry and how the car uses the batteries.

A partial recharge is not the same as a full recharge, however. If you only use 30% of a charge before you recharge the car and then recharge it, it only counts as one third of a recharge. So you might only be able to recharge a lithium ion battery 6,000 times, but if you recharge every time you use 30% charge, you'll likely to get three times that number of recharges.

This is all very rough figures, you understand, but as a basic rule of thumb, its good enough.

However, there is another issue. If you don't fully drain your batteries - at least occasionally - then the range of your car will start to decrease. Batteries like to be exercised every so often in order to maximize range. Ideally, you should aim to use the entire range of your electric car once every 7-10 days.
 
MikeBoxwell said:
Ideally, you should aim to use the entire range of your electric car once every 7-10 days.
This statement is subject to interpretation. I probably will never drive my Leaf more than 20 miles in one day, more often < 5 miles. Does this mean I have to find a chance to drive 50 miles or more every week or so, i.e. near the full range, or do you mean it is important to come near a full discharge, but not necessarily at one time? In other words is driving 5 miles 10 times in 10 days, then recharging, qualify as "using the entire range", or is it important to do the discharge all in one trip as implied by your statement? This could actually be a deal killer for me if I had to get in the car and drive around for a couple of hours once every week or so just to keep the battery "healthy."
 
MikeBoxwell said:
However, there is another issue. If you don't fully drain your batteries - at least occasionally - then the range of your car will start to decrease. Batteries like to be exercised every so often in order to maximize range. Ideally, you should aim to use the entire range of your electric car once every 7-10 days.

Mate, your take on partial cycles VS. full cycles is spot on. But the need to fully discharge the pack is talking to 'memory effect' and that's not something lithium cells suffer from. From a cell standpoint (and within the protected limits of the management system) the pack won't care how many times a pack is partially charged each day.

There still might be a reason to run a full discharge once in a while, and that will be to reset the computer's sense of when it's empty, as it's indication -and the fuel gauge and miles remaining calculations - might drift over time. We won't know for sure how the management system and computers work until we get the cars. It could be a procedure that's done in the garage by running the heater until the pack is actually flat (not when the computer thinks it's empty) as is done in other production EVs from the 1990s/2000s.

Andy
 
Actually, it is true of lithium as well as lead acid, ni-cad or nickel metal hydride.

How many people buy a laptop computer and only rarely take it off mains power? After a year or so, the batteries are useless with only a few minutes life rather than a few hours. The answer is simple - unplug the computer at least once a week and run it on batteries until the batteries are running low. The result will be a laptop battery that will last for 5-10 years rather than giving up the ghost after 1-2 years.

It's true of every electric car I've ever driven as well (and believe me, I've driven a few) and bears up with the tests I've carried out with my Mitsubishi iMiEV. If I charge it up every night having done 10-20 miles, the computed range of the car starts to deteriorate over a period of 10 days or so until it is reporting a total range of around 60 miles. If I drive it so that I'm using most of the range once every week or ten days, the range stays up to over 80 miles. When I drove the car from Coventry to Oxford and back (120 miles with a quick top-up charge in Oxford) the car subsequently reported a range of over 90 miles the following day.

In a real world scenario, making sure that you occasionally end up using most of the charge normally isn't a problem. People's driving pattern change over the period of a week, so if you're only driving 5-10 miles a day during the week, the chances are you'll be driving a lot further at weekends, or visa versa. The chances are you'll be using much more of your range at some point during your usual weekly driving.

The alternative is also valid: if you only ever need to drive 5-10 miles a day, you can quite happily recharge your car every night and top up the batteries. Your range will deteriorate, but then if you're never going that far that won't be a problem anyway.
 
MikeBoxwell said:
Actually, it is true of lithium as well as lead acid, ni-cad or nickel metal hydride.

How many people buy a laptop computer and only rarely take it off mains power? After a year or so, the batteries are useless with only a few minutes life rather than a few hours. The answer is simple - unplug the computer at least once a week and run it on batteries until the batteries are running low. The result will be a laptop battery that will last for 5-10 years rather than giving up the ghost after 1-2 years.

It's true of every electric car I've ever driven as well (and believe me, I've driven a few) and bears up with the tests I've carried out with my Mitsubishi iMiEV. If I charge it up every night having done 10-20 miles, the computed range of the car starts to deteriorate over a period of 10 days or so until it is reporting a total range of around 60 miles. If I drive it so that I'm using most of the range once every week or ten days, the range stays up to over 80 miles. When I drove the car from Coventry to Oxford and back (120 miles with a quick top-up charge in Oxford) the car subsequently reported a range of over 90 miles the following day.

In a real world scenario, making sure that you occasionally end up using most of the charge normally isn't a problem. People's driving pattern change over the period of a week, so if you're only driving 5-10 miles a day during the week, the chances are you'll be driving a lot further at weekends, or visa versa. The chances are you'll be using much more of your range at some point during your usual weekly driving.

The alternative is also valid: if you only ever need to drive 5-10 miles a day, you can quite happily recharge your car every night and top up the batteries. Your range will deteriorate, but then if you're never going that far that won't be a problem anyway.


To regain the full capacity of Flooded nicad batteries they must go through a maintenance charge which involves draining them to zero, this sometimes requires leaving the heater on until the entire pack on only shows a few volts. Then the pack is greatly overcharged and water is added. Taking flooded nicads down extremely low and cycling them deeply at times is important to retain their capacity. I have a friend with a 22 year old Saft pack that still has very good capacity and runs strong, they are amazing batteries.
 
Keeping in mind that the battery management system in a laptop, and the cell chemistry in a laptop, are vastly different from automotive systems:

My 3-year-old Dell laptop was connected to the charger constantly for the last 18 months. A few weeks ago I had to take the laptop on the road. The battery lasted 5 minutes before it went dead... but the battery was fine, just empty. After I charged it back up, it now runs over 5 hours. The management circuit just needed to be re-calibrated. It is possible (but not a given) that we may benefit by re-training the BMS in the Leaf from time to time--but the capacity of the cells won't be affected by this, just the management system.

There are no hard and fast rules for Li-Ion battery storage. Each chemistry has its quirks. Generally, for laptops (and phones, etc.), storage at 50-80% SoC under refrigeration will slow the inevitable self-degradation of the pack. There is no memory effect, but repeated, full charge/discharge cycles will wear the packs faster. Laptop battery management is designed to allow a much deeper discharge and fuller charge than we'll get with automotive cells, so a laptop battery will only last a year or so if you deep-cycle it frequently, or if the charge circuit isn't smart enough to shut off entirely when it's not needed. (No trickle charging.)

Nissan has been working with automotive Li-Ion for longer than anyone else, and I expect they'll have a product designed to work well and last a long time, without being pampered. I expect that the majority of degradation that will happen over time is the natural degradation of the Li-Ion chemistry, and there probably isn't much that can be done to slow it.

Nissan wants this car to be mainstream. I'm sure they realize that it has to "just work." Mitsubishi clearly doesn't have the same ambition.
 
Bicster said:
Nissan has been working with automotive Li-Ion for longer than anyone else, and I expect they'll have a product designed to work well and last a long time, without being pampered. I expect that the majority of degradation that will happen over time is the natural degradation of the Li-Ion chemistry, and there probably isn't much that can be done to slow it.

Nissan wants this car to be mainstream. I'm sure they realize that it has to "just work." Mitsubishi clearly doesn't have the same ambition.

Hmmm. Not sure I share your optimism there. I've talked to engineers who have worked with automotive Li-Ion for over ten years and I was involved with li-ion battery management on handheld computers in the 1990s.

Yes, the chemistry between a laptop battery and a car battery are very different. However, the LiFePO4 batteries in an electric car do have certain characteristics and one of them is that if you frequently charge the batteries without allowing them to discharge occasionally, you'll get less capacity from those batteries. It isn't a permanent effect and you resolve the problem by driving the car until the batteries are low and recharging it a couple of times. You can limit some of the effect through clever software, but even then there is a limit to what you can achieve.

You'll also get a significantly reduced capacity from the batteries in extreme cold conditions. You can reduce this effect by keeping the batteries warm, which is why most electric cars will have battery heating systems to keep the batteries warm in winter, and again it is amazing what you can achieve with some clever software. But I'm yet to come across an electric car that doesn't have a reduced range in a cold European winter compared to a warm summer day.

darelldd said:
Andy beat me to it.

With a Li pack, you will NOT want to drain the pack any more often than you must.

Absolutely correct, but guess what? You don't have to worry about that. The software management in the battery pack stops you from over-discharging the batteries.

To be fair, most of this is a technical discussion that most people won't need to be worried about. You don't need to pamper the batteries because what happens in reality is that the car does what you want it to do: if you only use your car for pottering 2 miles to the shops and back before putting the car back on charge, your car will do that perfectly fine. If you use your car for longer 50-60 mile journeys, the car will do that as well. The only time you may notice an impact on range is if you use your car for pottering to the shops and back for six months in a row and then attempt to do a longer 50-60 mile journey. And in reality, what is the chances of that actually happening?
 
The Leaf does have a heated pack.

There seems to be a lot of circumstantial evidence that the actual LA4 range of a new Leaf is closer to 135 miles. I think Nissan is being careful not to promise too much. It's easy to see why over-promising would be a mistake. Nissan wants to sell 500k Leafs in 2013. They are playing to win.

Where's AndyH?
 
If Nissan have overspecced the battery pack, that is how they're going to achieve the range and consistency. They can use clever software management to deliver the range and consistency that is required time after time after time.
 
Bicster said:
The Leaf does have a heated pack.

There seems to be a lot of circumstantial evidence that the actual LA4 range of a new Leaf is closer to 135 miles. I think Nissan is being careful not to promise too much. It's easy to see why over-promising would be a mistake. Nissan wants to sell 500k Leafs in 2013. They are playing to win.


If that were true, it would certain help alleviate the (minor) range anxiety I have going in.
 
There are 5 significant issues:
1. Differing battery chemistries (even the many different "Lithium Ion" types) vary greatly in how they should be treated for long life. For example, some can tolerate over-charging, but most do not.

2. Good (or "best") cell and battery pack management strategy is often critical, and many times neglected, often due to cost or complexity. However, I suspect (strongly hope) that the LEAF will include very good cell-level battery management. I suspect Nissan is able to do this, due to their long experience with (their version of) LiMn chemistry, and their desire to have the LEAF run well over time. Avoiding over-charging and over-discharging of each individual cell (48 x 4 = 192 cells) is a primary function to keep the cells in good health. Then, keeping the cells "balanced" (at a uniform state of charge) is necessary to maintain good battery pack "usable energy" levels (thus, good car range).

3. Actual energy storage capacity of the cells, which might change over time, sometimes increasing at first, but usually decreases over the long term. Most of the Lithium chemistries seem to be pretty good in this area.

4. The amount of usable energy "lost" as you take energy out of a cell, varies with the discharge rate and with reduced temperatures. These occur on "all" cell chemistries (known to me). Higher discharge rates usually make the effective cell voltage decrease, so the "energy" extracted (watts (power) = Voltage times Current) decreases when "pulling" high currents from the battery. Lower temperatures tend to slow down most chemical reactions, so usually a "cold" battery is (sometimes significantly) less "able" to deliver power. Too-high temperatures can also cause problems, since most cell chemistries have some high-temperature limitations. The newer Li chemistries are MUCH safer at high temperatures than some of the earlier Li types, so there should be no real worry there. But, some performance reduction can be expexted at the temperature extremes.

5. The controller's "estimation" of the available energy (sometimes translated into an estimated range) can be terribly inaccurate, and even falsely limit our use of the battery (as in some laptop batteries). Then, it is the software that needs to be "reset", sometimes only done be almost draining the battery, even when there is no real reason to "drain" the battery.
 
Bicster said:
The Leaf does have a heated pack.

There seems to be a lot of circumstantial evidence that the actual LA4 range of a new Leaf is closer to 135 miles. I think Nissan is being careful not to promise too much. It's easy to see why over-promising would be a mistake. Nissan wants to sell 500k Leafs in 2013. They are playing to win.

Where's AndyH?

Let's say your goal was to travel as far as possible and you had the ability to chose how you drive. What is ideal? Constant 30 mph?
 
LTLFTcomposite said:
Let's say your goal was to travel as far as possible and you had the ability to chose how you drive. What is ideal? Constant 30 mph?

Nobody knows, but probably something close to that. Where are you going with this?

I wish Nissan would just dish out the 411 already!
 
Most likely higher tire pressure and a steady 25 mph (possibly the 20 to 30 range) will work best when on level ground.

Some hypermiling techniques (like pulse and glide) might do better than "constant" speed, but others will know that answer better than I.
 
Bicster said:
LTLFTcomposite said:
Let's say your goal was to travel as far as possible and you had the ability to chose how you drive. What is ideal? Constant 30 mph?

Nobody knows, but probably something close to that. Where are you going with this?

I wish Nissan would just dish out the 411 already!

Wondering if the 100 mile number could be substantially exceeded under the right circumstances vs being best case and most scenarios would fall short. If I know what's optimal I can be cognizant of how far I'm deviating from it.

In spite of all the testing it won't be until these things start getting into users hands that they'll really know what the performance affecting factors are. Presumably the car will record its charging and usage history and Nissan will derive the trends from all that data.
 
If Nissan has overspec'd the battery, there are a couple of possibilities:

1) Substantially more than 100 mile range (135?) with unaggressive city (LA4-type) driving, in temperate weather on flat roads. Over time this degrades to 100 miles. You might even get 200 miles of range without accessories and constant 30mph or so. E.g., on a dynamometer.

2) The BMS lies about available range and attempts to give us ~ 100 miles even in adverse conditions. This is a lot harder to pull off and I think it's less likely.

Since we've seen a few dash photos of the Leaf that seem to suggest #1, I'm hoping for that.
 
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