How can we calculate a single “performance score” for a cell? Something everyone can use to easily choose between multiple cells for any application.
Is it even possible?
I’ve been thinking about it for years and I’m still not sure how I would want to calculate it. I wanted to see what you thought as it sure would be handy to have.
It could even be a power vs energy score, where a score for both types of applications was given. For example…
P95/E75 would be the Performance Score for a great power cell.
P55/E97 would be a great energy cell.
P80/E80 would be a good overall cell.
P55/E55 would be a crap cell for anything.
It could be based on the DC internal resistance (IR), Wh delivered at different power/current levels, measured capacity at the nominal low current level, max temperature, and/or estimated current rating. Cycle life is critical but too hard to measure as even a quick number for comparing cells with would take about three weeks to get for each cell type. And you can’t test just one cell of each type. I would need a bookcase full of cyclers and that costs a fortune.
Size and weight are critical for many that are looking for a cell (Energy Density and Power Density). How do we incorporate those into a single score with performance? Probably not possible?
It might have to be just a performance-based score along with size, weight, and the two densities that are used to choose a cell?
For me, the delivered-Wh at different power/current levels is the most important performance metric. But the max current rating will always been needed. The cell with the highest delivered Wh at one power/current level can easily not be the best cell at another power/current level. How can we represent this cell’s performance with one number? Is it even possible?
I’m hoping y’all have some good suggestions. I’m dying to condense my tables and reports down to something easier to use, faster to read, better for choosing the “best” cell with. Any suggestions you have are appreciated!
Personally I would love a website that allowed you to directly compare the discharge charts of cells at different power levels. Currently I kinda just read the numbers / compare the graphs in photo editing software.
In the ideal world (i.e., going forward) when choosing a cell, I would probably look at the rider’s logs to figure out what’s their average power consumption, and what’s their peak, and then out of all the cells that can provide that peak power level without overheating, pick the one with the largest capacity at the average power draw. (Unless the build has specific weight / longevity / price requirements, where I would need to take other factors into account as well)
Im not sure that it’s possible to condense the needed info about a cell any further than your excellent ratings graphics already do. A really condensed number would require the reader to have a decent level of knowledge of batteries to interpret/understand.
What’s the use case for this performance rating? Knowing when you might use it may help us to determine what info is needed.
I’m not a huge fan of singular score percentages, if only for the fact that it doesn’t stand up over time. I think it’s safe to assume that battery technology is going to get better over time, so you’ll need to constantly revise older scores downwards to make room for the changing performance ceiling.
Everyone just wants to know what the “best” battery is. Since availability is so spotty, and price so variable, a performance score can allow someone to decide what is most important to them when they shop. The performance score makes it easier to weigh that against price and availability.
It will also help to reduce the number of questions I receive each day, roughly 150-200. The vast majority of them are some variation of “what is the best battery…”.
In my testing (three different times over a year or so) the production 40T did a little worse than the P42A though. But not enough to be noticeable IMO.
A lot of this is luck of the draw since all cells from the major manufacturers (except Molicel and the China factories) we buy are excess inventory and unauthorized sales of cells in unknown condition.
That’s only if I use some sort of limited scale, like 1-100.
If I use a limitless number based off of some equation involving the performance results then it can be at any level and not need scaling over time.
when technology advance, and newer design / material is used, 100 won’t be the ceiling (yea…im looking at u dxomark) of how u score a cell unless there is a way to adjust the score to fit older production cell into the 100 scale when newer cell shows up on the market or when daddy elon had a few too much and pour his own lithium cocktail
I worked on that kind of rating earlier but ran into problems when I found out some didn’t care about one particular bad spec but really cared about the others. Unfortunately, when you mixed everyone’s priorities together it resulted in none of the specs mattering.
A lot of people have also asked me, after hearing about one or more specs being bs, whether the cell still performs well at its actual performance level. That is, the ratings accuracy didn’t matter if the cell could still be used for something and was inexpensive.
The fact that the company lied to them to make a profit was of no concern to a lot of people.
I personally still think some sort of ratings accuracy spec is good (because I hate the ratings bs so many companies practice) but I’m torn whether this rating would be of real use.
For the esk8 community, I agree.
The Recommended Batteries tables are unfortunately far, far too complicated and technical for the vast majority of the flashlight and vaping communities. Particularly the latter.
We can often forget just how knowledgeable we are. Even knowing that a 21700 is larger than an 18650 is something most people looking for the best battery don’t know. Or even that 18650 and 21700 are battery sizes.
This probably means I have to do different things for different communities. Hopefully not though. I’m trying to find a way to simplify what I’m doing now, not add to it.