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Battery drain

Old 02-28-21, 02:19 PM
  #1  
kayakindude
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Battery drain

So I'm trying to understand battery drain. I would think a system that has bars to indicate the amount of usage would be pretty even. But on a 30 mile ride today that was not the case at all.

I kept the system on the lowest assist setting. There are 5 bars and the battery was fully charged. The 1st bar drop was 4.25 miles in. The 2nd was another 4.5 miles in. At that point I was sure the battery would give out before completing the route. Now here is where it gets weird. The 3rd bar drop was another 11 miles in, more than double the drain rate of the first two. The 4th bar drop was just under 7 miles and we still had a remaining bar when we finished at just under 30 miles.

Our speed was pretty consistent throughout the ride- see below




So why would there be such a huge difference in drain between mile 9 and mile 20? Is that normal with an e-system?
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Old 02-28-21, 03:04 PM
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its normal for lower end batteries they drain faster as they drain. plus the bars are not real accurate. my bosh is pretty consistent and it has percentage and tells you have much distance you have left. but even then it drops a little faster as it gets lower thats just batteries for you. but I have the same amount of assist till the battery cuts off.
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Old 02-28-21, 03:33 PM
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What parameter is actually being measured on those little battery icons?
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Old 02-28-21, 03:36 PM
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Originally Posted by skookum View Post
What parameter is actually being measured on those little battery icons?
cold be voltage or battery drain percentage whatever the manufacture choose. its usually not super accurate. it takes computer to calculate it out accurately.
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Old 02-28-21, 03:45 PM
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Originally Posted by fooferdoggie View Post
cold be voltage or battery drain percentage whatever the manufacture choose. its usually not super accurate. it takes computer to calculate it out accurately.
Well voltage can be measured fairly easily, but is the voltage drop linear? Maybe it is in the portion of the curve that we are interested in?
But how is "battery drain percentage" measured?
I never look at the little battery icon, it doesnt seem to convey useful information, I look at the voltage and the watt hours.
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Old 02-28-21, 03:50 PM
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Originally Posted by skookum View Post
Well voltage can be measured fairly easily, but is the voltage drop linear? Maybe it is in the portion of the curve that we are interested in?
But how is "battery drain percentage" measured?
I never look at the little battery icon, it doesnt seem to convey useful information, I look at the voltage and the watt hours.
even then it does not let you know how much range you have. my bosch tells you how much range you have in any assist level and its pretty accurate usually you get a mile or two when it says zero unless the terrain changes a lot all the time like more hills then it may under report the range a bit.
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Old 02-28-21, 05:57 PM
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I presume its a calculated value rather than a measured value. How is it calculated? You could take the watt hours consumed since the battery was charged, subtract that amount from the fully charged amount and then divide by the average watt hours/ km and get a range value. But you generally dont want to run your battery down to zero.
I am assuming somebody on here knows way more about it than me and can tell us.
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Old 02-28-21, 06:52 PM
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Originally Posted by skookum View Post
I presume its a calculated value rather than a measured value. How is it calculated? You could take the watt hours consumed since the battery was charged, subtract that amount from the fully charged amount and then divide by the average watt hours/ km and get a range value. But you generally dont want to run your battery down to zero.
I am assuming somebody on here knows way more about it than me and can tell us.
most batteries will cut off before then. or the controller will kill the power. but the problem is there are lot of variables to it what level assist how much you peddle what the terrane is like the weight of the bike. it needs good computer to calculate it. bosch has it built in I think specialized uses your phone to tell you the range. but most bransds that have a hub drive don't have any of that info. there may have wattage or lots or such.
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Old 02-28-21, 07:18 PM
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For me it's not critical because we can just continue without assist, but I just assumed the bars would work similar to a smartphone...if the variables are consistent, then the drain should be too. Over 30 miles the weight, speed, and for the most part grade, were pretty consistent...yet the bar segments were not.

The battery is advertised as having a 25 mile range and it surpassed that pulling more than twice the weight it is designed for so that is great, just have to settle that the display bars aren't accurate.
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Old 02-28-21, 08:12 PM
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the higher end mid drives will have a more even drain and they wont suffer less assist as the battery drops. but after awhile you will know much much range you will get. like on our tandem on a fairly flat bike path 15 miles each way we will use more battery getting to one end as it has light 1% grades here and there coming back we cruise at 18.5 or so where the motor is hardy helping at all and we use less battery but if we can keep it at 18.0 we got a lot more range.
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Old 02-28-21, 09:22 PM
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A friend was telling me that her hubby always runs out of battery before she does. They have identical mountain bikes and are riding in steep terrain and he weighs considerably more than she does.
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Old 02-28-21, 10:15 PM
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The battery bars are not accurate and are a measure of voltage. Percent voltage drop does not equate to percent of watt hour remaining. Watt hours is also not accurate for battery drain because of battery voltage sag. Amp hours used and remaining is usually the most accurate indication of remaining range.

One nice thing about battery percentage is that the battery cutout at 20% remaining battery is done on voltage. The actual remaining battery power left is much lower than 20%. More like 5-8% remaining. You are actually getting more than 80% of the battery amp hours when the battery cuts out. You are not wasting 20% of the available battery power.
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Old 03-01-21, 12:56 PM
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I usually get about 100km per charge, city riding, some short hills, stop and go.
Cycle Analyst is telling me about 10Wh/km, which is a bit high for me, I have an 828 Wh battery, but I try to charge only to 80% so to get 100km, my Wh/km should be lower.
I recharge when the battery voltage reads 32, or I reach 100km, whichever comes first..

36V 23 Ah battery

ebike range calculator here;
https://www.ebikeaholic.org/ebike-range-calculator

It doesnt work well for me
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Old 03-01-21, 01:08 PM
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Originally Posted by KPREN View Post
The battery bars are not accurate and are a measure of voltage. Percent voltage drop does not equate to percent of watt hour remaining. Watt hours is also not accurate for battery drain because of battery voltage sag. Amp hours used and remaining is usually the most accurate indication of remaining range.
Battery bars typically measure voltage and can be accurate or inaccurate, depending on the correction applied. Li-ion battery drain is quite non-linear, the voltage drops very quickly at the start and end, but is fairly flat in the middle. It's very simple to correct for, but if the manufacturer is lazy they won't necessarily. The correction curve depends some on the exact batteries, so it's more likely to happen on a fully built bike. My Bafang allows for 52V settings, but the battery bars are still scaled to 48V and assume a linear discharge.
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Old 03-01-21, 01:40 PM
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The bars on my Yamaha equipped Haibike seem to agree with the % numbers which are delineated individually on the display.
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Old 03-01-21, 08:27 PM
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Originally Posted by 2old View Post
The bars on my Yamaha equipped Haibike seem to agree with the % numbers which are delineated individually on the display.
my bosch will give me the miles I have left and the percentage. its only off a mile or so always on the lower side so your not stranded.
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