Percentage of discharge?

[Marley]

Have the Bosch system and was curious of your habits.
I understand that a complete discharge can reduce the lifespan of battery but was wondering if a recharge is necessary after each ride.

If not, what is an optimal range of discharge before recharging.
Thanks

 

[steve_sordy]

Apart from a short trip around the village I can't recall EVER riding the bike without topping up the battery.

 

[DtEW]

Either a complete discharge or a complete recharge will reduce the lifespan of a lithium-based battery. In fact, it’s a function based around how far you take the state-of-charge (SoC) away from some point near the center (50%?) that proportionally reduces its lifespan.

This is why in electric car communities, even given the advanced automated battery management (cell balancing, etc.), but with the prohibitive cost of replacing the battery... it is generally agreed that daily-bread-and-butter use is best limiting charging to 85% SoC (for those unfamiliar to electric cars, all of them have this setting and others in their energy management). You don’t charge to 100% unless you really know you need the range that day... and you most certainly don’t keep it at that SoC for long. It is also advised that you aim to keep from discharging below 40% SoC, but I’m sure that’s with a built-in margin accounting for range anxiety.

Here’s some interesting stuff.

BU-808: How to Prolong Lithium-based Batteries

BU meta description needed...

batteryuniversity.com

Although the entire article here is worth reading, Table 2 stands out. Increasing your depth-of-discharge (DoD) from 40% to 60% more than halves your battery’s cycle life, and increasing your DoD from 60% to 100% more than halves it yet again.

Here is a summary of best-practices when it comes to maintaining a Lithium-based battery.

Explaining the Do's and Don'ts of Battery Charging - Battery University

Discover ways to extend battery life by following simple guidelines

batteryuniversity.com

I don’t use a Bosch system (I own 2 Specialized Levos), but for bread-and-butter rides, I charge to ~90% the-morning-of (basically I plug the bikes in the moment I wake up and set up timers on my phone). The worst I’ve managed in terms of DoD is that by the end of a ride I’m at 30% SoC. When I get home I plug it in (again, timed on my phone) and take it back to ~40-60% SoC. And that’s how my bikes will be stored. People (might even be here, some years ago) have worked out a very good formula that describes the charging behavior/curve of the Specialized system... but I can’t be bothered to calculate. My mental rule-of-thumb is that it adds roughly 10% charge for every 20 minutes charging, at least at the SoC range I work with. The Bosch is a popular system, so doubtlessly somebody has worked out the behavior/curve as well somewhere (?)

Yes, it would be nice if e-bike systems allow limiting the maximum SoC like electric cars do. But so far the industry approach (or maybe just Specialized’s?) is only that of disposable consumer electronics... which I guess works OK for them given that e-bike battery warranties aren’t at all comparable to that of electric cars’, eg. 2 years for a Specialized/Bosch vs. 8 years for a Tesla/GM. It is notable here that Specialized’s battery warranty is on par with that of “small wearable batteries” (300 cycles, Bosch does better at 500 cycles), and not even that of smartphones (800 cycles), not to mention that of electric cars (5000 cycles; this is only a design goal to achieve 1 million miles, the warranty itself is only reliant on age).

 

[Slapbassmunky]

All the info DtEW gave is very good, if a little overkill for an ebike. As has been said, they like to be stored at around half charge and at room temperature or cooler. Keeping them topped up to 100% and hot storage temperatures will kill them much faster. Think about this if you leave your bike in a scorching hot shed or workshop in the summer months.

I had my old bike for over 3.5 years, I stored it around 50% and fully charged before each ride, then made sure to top it back up to 50% ish before storing the bike again. If I still had 4 bars left at the end of the ride because it was cut short, than that's no big deal either, I just didn't charge it when I got home. I didn't notice any range drop off at all for the whole time i had the bike. Remember that cells will drop off with age as well, regardless of how well you treat them.

For perspective, at 2500 off road miles I roughly calculated that my first pack had done 80 cycles.

If you run the pack down to the point of cut off its important to charge back up to 50% as soon as possible.