Actually it's not the temperature swings that would have a negative impact, it's the Heat. Heat is what kills Li-ion batteries, and that final 10% of the charging cycle is what builds up the most heat (as does baking it in a car).
R2
Why would the last 10% create the most heat? During this the current is reducing towards zero.
Probably it's accumulating more slowly but is adding to the heat already there from earlier charging, until the cooling to ambient temperature is faster than the warming from charging. This would be another reason to charge slowly instead of quickly. Heat could dissipate while charging. I have a feeling Canon have figured all those details out and taper off the charge appropriately.
Thanks Victor, I didn't have time to explain any more thoroughly (had to head to work). The heat accumulates the most by the end of the charging cycle. It's very bad to charge (or keep charging) a hot battery!
It won't be hot R2. The charge currents are small.
The current is tapered as per the expeditions of the cell manufacturer until the expected cutoff, probably around 30mA.
It is quite plausible the end of the cycle isnt the point of maximum temperature for a cell, and it would be unusual if it was. So I don't think this is the right way to view it.
Look at the last line in my post (which you ignored ;-) ). That of course describes Canon's circuitry (which prevents cooking of the battery during charging). However I've seen other 3rd party manuf that don't do so well!
In addition there are other factors that can come into play that will change the heat production curve of the charging cycle, such as immediately charging a hot freshly-depleted battery, or charging a battery when the ambient temperature is high. Every manuf I've seen recommends against doing either of these.
Discharge is even worse. The heat generated internally gets very high (due primarily to the increased internal resistance) as the battery gets depleted.
If we notionally say we will pull 25W, or 3A and power will reduce the temperature of the battery should be thought about as a delta from its start point. So assuming it will be hot I also don't think is correct.
Look at any temperature test curves done on Li-ion batteries. You'll see that huge spike at the end of the discharge cycle. Or just feel the thing with your hand!
I looked for such a curve but didn't find one. I do notice my laptop warming up when it is charging. I've not noticed it with Canon batteries, but I don't have them sitting on my lap when they're charging either.
It appears that discharge is what R2 was thinking about, but maximum rate of charge also won't be at the end of discharge.
There are a lot of thermal models used related to both the analysis of entropic charging but also being able to monitor/predict. For example in a car we implement certain cells discharging, other cells used in regen to better equalise the thermal energy within a pack. This is to improve performance rather than longevity
There is an open paper called something like thermal analysis of a fast charging method for high power lithium ion cells. That gives some description of ways in which thermal impacts to charging are taken into account when one wants to fast charge.
Ephemeris, you’re clearly very knowledgeable about, and professionally involved with, battery and charging technology. I asked a question earlier that I don’t think has been answered.
Main question: What do the three bars (3 green, 2 green, or 1 red) displayed on the battery info screen actually represent?
I posted a few responses along the way of what Canon said it was in one of there kind of info papers and also from the R7 manual (I was reading it at the time).
This is from an old EOS magazine.
What information can your Canon EOS camera tell you about your camera battery performance? We hit the 'Battery info' button and reveal all.
www.eos-magazine.com
This is from the 1DX MKiii manual where it appears the charger has the recharge performance display.
Is this a state of health parameter Canon describe? I'm not sure. Perhaps the charger times how long it takes to reach the voltage control limit in the charger cycle to use it as an estimators for how much charge is stored.
Perhaps even more simple is a voltage measurement at the current cutoff at end of charging.
I'm not sure.
I'm also not sure how that's transferred to the camera. Or does the camera form a simple current measurement by passing a 1kHz AC across the cell to use as an estimator for battery resistance?
Sub questions : Are they an actual measure of “recharge performance”? If so, how is that being measured, and how/where is that information stored? On the battery IC or in the camera? Logic would suggest in the battery IC as it reads the same in different camera bodies. Or is it a “counter”, simply documenting the number of charge/discharge cycles? Or something else, such as state of discharge before recharging? Or measuring increased internal cell resistance as the battery ages?
I would think if this is passed digitally to the battery from charger , and then to the camera then we should be able to measure that data on an oscilloscope. It would seem a complex way to do it.
Counter. Perhaps but then one still needs to transfer the data. Perhaps they do.
Measuring the resistance would be easier I'd think.
Canon clearly wants us to buy a new battery when we see one red bar, yet the batteries continue working.
It seems like it's something they have had as a feature for a long time (perhaps before 1Dx Mk iii).
Questioning it's usefulness seems reasonable. I also have some batteries showing red but that's doesn't preclude me from using them. How they compare to a new for some simple charge / discharge graphs I suppose may help us a little but I think that just says I'm testing an older lithium cell compared to a new one so I should be able to anticipate the result before doing any work.
I think power from these batteries is a problem. Notionally there a circa 25W battery when new and charged. But at what point in the state of charge // life span does some of the camera features shut down? 8k /4k120 perhaps, or high frame rate shooting.
I run grips on the r5s but the camera doesn't appear to be able to use them concurrently and keep that available power level up for longer.
We develop some power tool batteries (the models for them) and say we have a 2000W tool then long before the battery is depleted you don't have a 2000W tool any longer as the system is power limited by the battery.
