I did some math and guess what, I came up with 1.6-2.3X cost difference if the full lifespan was increased by 3-4X. Why? Because of the higher price of the battery that would be required to do the same job at 40% battery 3, 60% battery 2, compared to 80% used from battery 1.
I used... https://www.pingbattery.com/

1; 48v 10Ah, $382. at 80% used can go 19.2 miles

2; 48v 15Ah, $533. at 60% used can go 21.6 miles.... 1.6 more battery #1 is required.

3; 48v 20Ah, $658. at 40% used can go 19.2 miles... 2.27 more battery #1 is required.

So, is that still worth all the time and effort, special charger, extra money up front? Just wondering.

How long will it take you to reach 400 cycles if you charge to 100%? If it's several years than probably not worth it. If it's a year or two and you think you'll still own the bike at that point it's worth it to pay more up front for a bigger battery. Those upgrade prices aren't bad either. On the OEM e-bike side you're typically paying hundreds of dollars for those types of watt hour increases. The Luna Advanced chargers are all you need to charge to 80% and they run about $100.

I think most people would easily last 2 years on battery #1 in my example, thus every 3rd year they would need a new battery for $382. Thus my Question, the increase of 3-4X battery life is a no brainer... But the Repay for the money is only, 1.6-2.3X the #1 battery... So who is/would actually still do it.?

People seem to balk at buying bigger batteries all the time around here. And to buy a bigger battery and not get the extended range with it seems like a big/huge hurdle...

Amp hours and longevity may not be related. Perhaps it depends a bit on how deep of discharge cycles (40% discharge cycle sounds good).

However, another way to look at it. Say you have you 20 mile commute.

With the first battery, you drain it 80%, with a 20% reserve capacity.

Over time, that reserve capacity will decrease, so your 20 mile commute will eventually start draining the battery 100%. Any more, and you'll be pedalling.

With the more expensive battery, you drain it 40%, and have 60% reserve capacity. In theory, it will take longer to reach that magical 100% drained and 0% reserve capacity point.

Another rating is to look at the various discharge rates. The maximum discharge rate is typically close to 1C. So, your cheaper battery will discharge at about 10A (about 480w), and the more expensive at about 20A (about 960w).

And, like above, the discharge rate will decrease with both age, and battery charge. So, your more expensive battery will give you more power, especially as the battery ages, and is drained.

Will your route ever vary? 30 miles? 40 miles?

Anyway, personally, I tend to like to choose higher capacity batteries for my needs (not bicycle power).

I agree with you, pretty much every time a bigger battery IS better, for all the reasons you stated, It just is...

Problem is money, People would rather spend less than more, and in a way it actually works. Buying a new $382 battery every few years, is just more doable for most folks... And that is why I am wondering how many people do, or would do what it takes to get 3-4X more life out of their battery...

I would look at it more like how much per year are you spending on the battery. A $382 battery that only lasts a year is more expensive to run than a $568 that lasts four years under the same conditions. The extra range of the bigger battery is nice to have when you need it as well.

The average person is clueless on this topic so it probably doesn't factor into their purchase decision.

IMO, where it's a real consideration is the 400-500 watt hour batteries that are supplied with some OEM bikes, but cost $800-$1000 to replace.

That is true, all they care about is the battery "good enough" to do X amount of distance, and don't even realize that even if it is, brand new... It won't be, after a few years...

And your first point is what I am trying to establish. What/at what point if any, are people going to do what it takes to hopefully reach the 3-4X lifespan of a battery that "could" be achieved, even tho financially it's closer to the 1.6-2.3X for making your money back... IMO

Yes, I would jump at the chance to have BionX re-program my battery charger so I could pick what level of charge I want...


I mean I can do it manually, just unplug it when it reaches 80%, but... really? With todays choices that are available... Why not make it a choice, and it gets done automatically.

EDIT: In fact, I am still leaning towards BionX being "smart enough" to charge the battery in a way as to not loose any lifespan in the last 20% of the charge cycle, or, the bottom 20% for that matter, but I don't know... One would think that the BMS would just cut out, and not allow anything lower than the batteries limit of whatever it really is, 20% either end lets say, so as not to loose any charge cycles...

I would do it that way, "if" I was the engineer at BionX, cut out the middle man, so's to speak, no, I would not allow the owner to take the battery down to 0%, no, I would not fully charge the battery up to the point where lifespan is hurt... JMO

350, good chance that's what they're doing; for your sake hope so and you'll have several good years left.

I'm gonna say no.

My first battery, 4 years ago, was good for about 2000 charges, but lasted me a couple of dozen charges over about 2 years. Not sure what happened there, but off brand chinese batteries are not my friend now.

3 years later I could purchase the same watt hours in a battery 1/3 the size - which totally transformed my bikes.

Bottom line - battery technology is changing so fast - especially as cars get into the game, that what is nice now may not be so nice 2-3 years from now. 400 charges is plenty for most people at the rate technology is changing

C58, your answers are the gold standard, but I want the battery on my Yamaha to last as long as possible. I don't care if they produce a one pound battery 10X as powerful. Won't change the overall weight of the bike that much and it's already a 20 mph PAS with more range than I need.

OK so, who's doing both, keeping the battery above the 20% left and below the last 20% charged?

I have only ever done the try to not be going below the last 20%, I have always charged my batteries to the full.

That is another way to look at it too, other than the price of the new battery you would be getting way more for the buck, than keeping a battery for lets say 8 years and never using it to it's potential trying to make it last...

Real-world battery lifetime is very difficult to predict. It's something I'd love to see. Charging to full is not as bad as high drains, especially if the battery isn't stored for days at 100% charge. Tesla recommends charging to 90% for optimum life-span, with the comment that a daily charged Tesla is a happy Tesla.

Consider some scenarios for overall battery life:
48V 10Ah 80% discharge -- 400 charge cycles = 553 MJ of energy consumed
48V 15Ah 60% discharge -- 400 cycles = 663 MJ
48V 15Ah 60% discharge -- ~800 cycles = 1327 MJ

The larger battery is only cost-effective if you're able to get significantly more cycles out of it. Now, the whole point of the larger battery is to do just that, but batteries fail for other reasons than just gradual degradation.

The last thing is that batteries are improving significantly still both on performance and price. So the small battery might cost $382 today, but 2-3 years from now, when you need to replace it, it might only cost $250, for a lighter battery.

My general advice would be plan for a battery to last 2-3 years and replace after that. With improving technology and wear items, it seldom makes sense to spend for a 10 year lifespan. Especially for an enthusiast who is likely to want to upgrade in a few years.

I have to take issue with the math. The 3-4 "lifespan" in this case is the total amount of discharged electricity over the life. Therefore the total cost should be per ampere-hour, and at 4 times more for even double the price is a huge savings over time.

Taking this a step further, there are two ways to only use (for example) 60% of the battery. One is with a full charge and discharging it only to 40%. The other is only charging it to 60%. These two are not the same with respect to battery life, and we should actually take the range from the middle - the 60% would be from charging it to only to 80% and discharging to 20%. This last is the recommended policy and, apples to apples, results in the battery having five times the total use of electric power over its lifetime.

You'd be WAY ahead doing it this way, with the only downsides of carrying more battery and as someone mentioned, the battery still being alive in a few years when you want to buy the latest greatest. I'm not sure I buy the latter as a reasonable objection - batteries aren't changing all that fast, that you'd feel like your pack is obsolete in three years.

I believe that is what I used, to get the same amount of Ah out of the $382 battery you would need 1.6-2.3X $382 batteries for the 60% and 40% used from the bigger batteries. But maybe my math is not as good as it needs to be...

Maybe I'm not following your calculation, or missing what you're getting at. Can you clarify?

1; 48v 10Ah, $382. at 80% used can go 19.2 miles - how many charge cycles to 80%?

2; 48v 15Ah, $533. at 60% used can go 21.6 miles. - how many charge cycles to 60%?

3; 48v 20Ah, $658. at 40% used can go 19.2 miles - how many charge cycles to 40%?

cost per Ah = battery cost / (charge cycles * (percentage charge * battery capacity))

The Battery University paper had it at:
400 charges to 100%
1200 charges to 80%
3200 charges to 60%
(they didn't list 40%)

So using their claim, the cost per Ah:

for the 10Ah, 100% is $382/(400*1*10) = 9.5 cents/Ah used
for the 10Ah, 80% line is $382/(1200*.8*10) = 4 cents/Ah
for the 15Ah, 60% line is $533/(3200*.6*15) = 1.9 cents/Ah

It looks to me like the lifetime cost is half as much for the 15Ah @60% battery as for the 10Ah @80%, and almost one fifth the cost of using the 10Ah with full charging.

OK, I re-did it and got a different answer...

48v X 10Ah = 480wattHr X 80% = 384/20=19.2 miles per charge.

48v X 15Ah = 720WattHr X 60% = 432/20=21.6 miles per charge. "Supposed" to last 2.5X longer so.

48v X 20Ah = 960wattHr X 40% = 384/20=19.2 miles per charge. "Supposed" to last 4X longer so 4.0 48v 10Ah batteries.

OOoops... It works out to
2.5=2.8 X $382=$1069.60 instead of $533, is going to be 50% cheaper with the 15Ah battery used 60% capacity.
4.0 X $382=$1, 528 instead of $658, is going to be 57% cheaper with the 20Ah battery used at 40% capacity...

Thanks for the link, I had been looking for data like that. I was really curious to see how battery charging impacts life.

Using 100-25% charge (75% eff. cap) = 2100 cycles to 85% remaining.
Using 85-25% charge (60% eff. cap) = 4500 cycles to 85% -- 1.7x lifespan of 100-25 cycle
Using 75-25 charge (50% eff. cap) = 7000 cycles to 85% -- 2.2x lifespan of 100-25 cycle
Using 75-45 charge (30% eff. cap) = ~10k cycles to 85% -- 1.9x lifespan of 100-25

The effective lifespan actually goes down for lowest duty cycles. For example, compared to the 85-25 case, it takes 2 cycles of 75-45 for each 85-25 cycle, which means that its effective lifespan is ~5k cycles and very close to the 85-25 depth cycle.

TL;DR -- 85%-25% is basically the optimum for battery lifespan, anything else offers minor improvements at best.

So, does that mean the 3-4X longer life is BS? It's more like 1.7-2.2X.? That would make a huge difference in the numbers I used...

No, no. It's better than that because you normalized to a 20 mi commute and allowed the battery pack to get larger.
The fallacy that most people make is that keep the battery the same and simply use less of it, which means that you need to recharge more frequently. By letting the pack get larger, each charge cycle is an equal amount of energy so you can directly compare cycles.

So using the numbers from the paper and your values:

48v X 10Ah 80% usage = ~2000 cycles (75% was 2100 cycles, just guessing here)
48v X 15Ah 60% usage = 4500 cycles (2.5x lifespan)
48v X 20Ah 40% usage = ~8500 cycles (4.2x lifespan)

So even the mid-size pack should have roughly 2x the life-span and the largest pack is 4x the lifespan.

So, Again... Who IS doing the 20% bottom and 20% top not using and not charging thing.? Not one person actually said that they are doing or are going to do this...

With the numbers that ended up and (nobody has yet contested), why not do it?

2.5=2.8 X $382=$1069.60 instead of $533, is going to be 50% cheaper with the 15Ah battery used 60% capacity.
4.0 X $382=$1, 528 instead of $658, is going to be 57% cheaper with the 20Ah battery used at 40% capacity...

One issue is that the vast majority of chargers are 100% only with no indication of other charge points.
I know Luna Cycle advocates the shallower cycle. They sell chargers that are switchable 80/90/100%. Their chargers are about $60 more than a generic charger so I would imagine they only really sell to their customers. People tend to buy either the cheapest possible kit or fully pre-built bike, and if you're looking at the out to door price a smaller battery and cheaper charge are going to be significantly cheaper.

And for many people, the cheaper option isn't necessarily a bad thing. My co-worker purchased an ebike, which he occasionally commutes on. At his usage rate, he'll probably get 5-10 years of service from a standard 100-20% duty cycle.

I am doing it with my 500wH battery but I have a Cycle Satiator. I charge to 70-80% depending on how far I'm going. I have a bigger 840wH battery coming this month so the range hit of charging to less than 100% won't be as noticeable.