Time for the most boring topic ever.... battery health.
As reported in the TQ software my battery degraded by 10% in the past year of use (about 1% deg per 500 miles of max boost use) over 134 reported charge cycles (more on what that means deeper below).
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For a phone 10% deg a year would mean in 4 years 100% charge reported to the user would be equivalent to a new phone limited to 60%. On a phone? Whatever, its cheap enough, you just charge it more as you slowly use it through the day, and by the time it is bad enough to impact usability usually you have the itch to upgrade for other reasons.
However, on an e-bike significantly degrading a battery would be absolutely terrible, quite limiting to use and range anxiety, and given this battery is fairly large, proprietary, and integrated into the downtube swapping it out likely costs somewhere around $1.5k... ouch.
Sticking with the phone example I recently begrudgingly upgraded from a very light Pixel 5 ~150g to a Pixel 9 ~200g after waiting too long for phones to get lighter again which sadly never happened. I had purchased the Pixel 5 used and by the end its battery was at about 60% rated capacity as reported in AccuBattery. On that phone I never adapted my charging behaviors from near worst case and I saw around 10% deg per year much like this bike.
So I did some research down some wormholes. People who own an EV, whose batteries are an order of magnitude more expensive still, likely already live this so this knowledge can translate to other spaces. Most of this is common sense but deploying it well can be tricky. Basically, unless needed you want to limit your charge to closer to the middle of the battery (more specifics later), you want to charge at low temps, and at low power (largely related to lowering temps). However, if you deploy degradation mittigations you are effectively self limiting your battery to a degraded state. Therefore, many are dismissive to fully engage with improving charging habits as it sounds counter productive on the face of it. What many miss here is these mittigations should just recenter normal use but should also be totally disregarded fairly often in any situation when extra battery is needed for say a long weekend ride. If you just allow your battery to degrade you can't get the lost range back but with some preperation I likely will reduce battery deg from 10% a year to 2% or less.
Continuing the phone example by deploying mostly best pratices I'm now expecting around 1% a year battery deg on my Pixel 9 instead of the 10% I had on my Pixel 5. Critical details here are the battery cycles per time (day/week/year), charge limit, charging temp limit, and charging power all of which are reported for a phone through Chargie hardware (~$25) or AccuBattery software ($0 - $4) with basically no options on either side for an ebike. Also not shown but very important to finding the right charging behaviour for a given user without overly impacting user experience is the % charging typically starts at.
While getting high 10% a year deg on my bike and Pixel 5 I would just charge to user reported 100% whenever I was done with the device. For my phone this was charging to 100% every night regardless of how much battery I used and on the bike I would typically get down to 10-20% for a fun ride and then plug the bike in while still hot which during the summer often would display overtemp warnings. What temp is this at? No idea they don't report any of this stuff to a user... error 4407 get stuffed anyone without internal unshared TQ documentation.
All of these charging behaviours detailed above offer less percent charge per battery cycle per AccuBattery "efficiency" numbers explained below:
This is where most people tap out on trying to deploy mitigations and I don't blame them. If you want the best battery cycle to wear charging efficiency you would only use your battery from around 47% to 50% [for most current high density battery chemistries] and then charge back to 50% but thats basically just running hard wired which is obviously impractical. However, perfect is the enemy of good so AccuBattery caps their "Efficiency" score at 887% which I've seen from limiting max charge to 65% or below. This % cap works for my phone because in a typical day I use around 40% (+5/-20)% which keeps me from ever dipping below 20% in a typical day. If I need more charge on my phone I just plug in to unrestricted charging to top off for a few mins. I'll also occasionally charge up to 100% if I am traveling internationally or something else when I don't want to be limited. In those situations a few times a month even if I dont need it the full charge it is nice to have it all charged up and unrestricted. Therefore, on the phone for my normal use case I can comfortably set a 65% charge limit on my Chargie and safely not monitor my battery % through the day and keep my battery very healthy. Meanwhile, on the ebike I use around 80% in a typical very hilly lunch ride meaning I really cant deploy any mitigations without limiting a ride or magically expanding the battery.
Oh wait external battery exist which add 50% user reported extra charge! With an external I can use 80% of the internal and 80% of the external battery and still get to 120% user reported. However, my internal battery was degraded to 90% which makes this (80*0.9+40)% = 112% effective charge getting me back into a usable range while helping mittigate further degradation.
At the end of the day any use will degrade the batteries but with some planning a user should be able to significantly reduce additive degradation to extend battery life. Unfortuantely there currently is no ecomonical way of restoring any battery degradation.
More on charging later this post is already way too long.
