E-Bike Battery Guide

[Ravi Kempaiah]

Ravi, My habit is to just bring the bike in and leave my battery rest so long as it is over 25% at the end of a ride. I then charge to 100% starting in the early morning before going out on a ride. This avoid my battery ever sitting above 80% for more than a couple of hours. Thus far, after putting up to two years and 6000 miles on one of them, it seems to be holding near the same charge as when new. Does this battery strategy seem okay to you or am I risking a significantly shorter battery life?

That is pretty much what I do on my bikes and at this rate (~8000 miles/year), I am estimating, I can get 50,000 miles before the batteries need replacement.
I am sure you will have similar results.

 

[Scotsman]

I received my first e-bike a week ago (a Rize City 48V 13AH model), so I don't have much experience with this mode of transportation. Prior to getting my e-bike I did a fair bit of research on e-bikes in general and battery charging in particular and have reached the following conclusions - I would welcome any comments, additions or corrections:

1. If you want to maximize the distance travelled or are suffering from "distance anxiety", and don't want to pedal a bit harder, then charge the battery to 100% of capacity after every ride. No harm will come to the battery in doing this, but the downside is that it will reduce the number of charging cycles available during the lifetime of the battery.
2. If you are more concerned with maximizing the number of battery charging cycles over its lifetime, then only charge it to about 80% - about 51.5 volts for a 48 volt battery, and try not to let the charge fall below 20% or so.
3. Fully charge the battery at least a few time during the cycling season to balance the cells.
4. Let the battery cool off for about a half hour before starting to charge it.
3. Batteries do not appreciate extremes in temperature, particularly if it is in a hot environment.
4. If you are attempting to charge the battery to 100% you may have to charge it longer than the advertised charge time to reach full capacity. For example, after a 30 kilometer ride yesterday my 48 volt 13 ah battery was down to about 50% and showing 46.8 volts on my multimeter. It took about four hours to reach 100% (54.3 volts), at which point the 3 amp Rize charger green light came on and the fan stopped working.
5. Try not to leave the battery at a 100% charge for longer than a few days and maintain a 50-70% charge if storing for an extended period - you may have to top the battery up a few times during that time to maintain that level of charge, since batteries naturally lose of their charge over time.

Since I am a retired senior rider, using the bike for recreation only and not really interested in marathon rides, I will probably go with point number 2 above for battery charging.

 

[Lightning P38]

I received my first e-bike a week ago (a Rize City 48V 13AH model), so I don't have much experience with this mode of transportation. Prior to getting my e-bike I did a fair bit of research on e-bikes in general and battery charging in particular and have reached the following conclusions - I would welcome any comments, additions or corrections:

1. If you want to maximize the distance travelled or are suffering from "distance anxiety", and don't want to pedal a bit harder, then charge the battery to 100% of capacity after every ride. No harm will come to the battery in doing this, but the downside is that it will reduce the number of charging cycles available during the lifetime of the battery.
2. If you are more concerned with maximizing the number of battery charging cycles over its lifetime, then only charge it to about 80% - about 51.5 volts for a 48 volt battery, and try not to let the charge fall below 20% or so.
3. Fully charge the battery at least a few time during the cycling season to balance the cells.
4. Let the battery cool off for about a half hour before starting to charge it.
3. Batteries do not appreciate extremes in temperature, particularly if it is in a hot environment.
4. If you are attempting to charge the battery to 100% you may have to charge it longer than the advertised charge time to reach full capacity. For example, after a 30 kilometer ride yesterday my 48 volt 13 ah battery was down to about 50% and showing 46.8 volts on my multimeter. It took about four hours to reach 100% (54.3 volts), at which point the 3 amp Rize charger green light came on and the fan stopped working.
5. Try not to leave the battery at a 100% charge for longer than a few days and maintain a 50-70% charge if storing for an extended period - you may have to top the battery up a few times during that time to maintain that level of charge, since batteries naturally lose of their charge over time.

Since I am a retired senior rider, using the bike for recreation only and not really interested in marathon rides, I will probably go with point number 2 above for battery charging.

Your options seem right on the mark to me.

On most of my rides, my battery goes down to 60-80% of full charge. After a ride I just park the bike without charging the battery. When I plan my next ride, I plug in the charger about 2 hours before I am ready to ride, and the battery is usually 100% charged by then.
Some times if my battery display shows less than an 80% charge, I may charge it for an hour, and then top it off for an hour on the day of the ride.

So I am using your #2 Method on my 10 amp hr battery and 36 volt system.

 

[Scotsman]

I am slightly confused now - but that's par for the course! I took my bike out for a ride today starting with a fully charged 48 volt battery - 54.3 volts on the multimeter. I was somewhat surprised to see it go about 20 km with heavy throttle use before the battery started to dip below 100% on the display (that's good I guess) - of course it went down fairly fast after that. When I got home after a total trip of 25 km, the battery display on the bike showed 80%. After a few hours in the house, the battery is showing 89% on the bike display and measures 49.1 volts on the multimeter. That figure of 49.1 volts at 89% is quite different from the 51.5 volts that I had read should indicate a charge of 80%. I am guessing that if I had ridden enough to get to an indicated 70% charge on the bike display and let the battery rest for a few hours, then it might have shown closer to 80% on the display at something less than 49.1 volts.
I am going to resist obsessing over this, but it's interesting how variable the charge percentage and the voltage can be in trying to get the battery to an 80% charge..

 

[Ravi Kempaiah]

I am slightly confused now - but that's par for the course! I took my bike out for a ride today starting with a fully charged 48 volt battery - 54.3 volts on the multimeter. I was somewhat surprised to see it go about 20 km with heavy throttle use before the battery started to dip below 100% on the display (that's good I guess)

The problem is with the battery BMS algorithm of measuring the State of Charge (SOC).
Think of this feature as a fuel gauge. Gasoline fuel gauges in cars have been perfected over the last few decades but the fuel gauges for battery systems vary a lot.
Some of the inexpensive bikes make use of minimal electronics and the display shows some % but it is almost always inaccurate. Many of these systems (and displays) show 100% for a long while and then the drop happens very quickly and this catches many riders off-guard. This is not an accurate representation of the battery SOC.
You can remedy to certain extent by switching to voltage based display. If the battery SOC algorithm is not robust, what happens is: under load, it shows lower voltage value and when you park the bike, the voltage comes back up. Another factor is bike manufacturers not using properly matched cell with the bike. Low power rating cell under high load performs poorly.
To comment on your note, voltage based readings are a little better than % based readings. But, this issue of wrong SOC cannot be avoided totally until you replace it with a better battery pack with more robust BMS.
PS: you won't notice this issue in an electric car because they employ better electronics.

 

[Scotsman]

Thanks for your reply Ravi. From what I can tell by many of the commenters in this forum, your opinion can be trusted a lot more than what the BMS on my bike is telling me! I will try to put the battery through a couple of deep cycles before winter and see if that assists in giving more accurate SOC readings, but my hopes are not high, and I am not prepared to shell out more cash at this point for more sophisticated equipment.

 

[Petropoliskhan]

On My Giant Bike the App tells me more precisely what % Level I am currently at.

So I figured out a Formula to "Time" the % Needed.
(for my battery & charger)

It is as follows:

2.25 Minutes for every % of charge needed.

Example:
If Battery is currently at 32%
But I want it at 80%
Take 80% minus 32% and it Equals 48
48 X 2.25 minutes = 108 minutes
That is 1 hour & 48 minutes Charge Time

This formula gets me within just a couple percentage points every time....................

HOW AM I DOIN RAVI ?

Hi CSH!
Just tried it out on my new Stromer ST5 . Works like a charm ! Great Formula!!
You just saved me a ton of cash (expensive charger purchase , no longer required to properly charge my battery)
Thank you

 

[Piter]

I had a bad battery when I bought e-bike. My friend recommended me battery NP and i have been using it for 2 years. I ordered here

 

[almikel]

Hi,

this is a great thread - I've learned a bunch - thanks heaps!
I've recently purchased a Giant e-bike, and the LBS (and the Giant manual) recommended I fully discharge the battery every 3 months of so...after reading this thread I better understand this is not necessary

I'm planning to purchase another charger to be able to selectively charge to 80% etc...I'm using timers at the moment, which is fine for now.
A 2nd charger will allow me to charge at home and at work, just in case I run my battery too low on a group ride on the way to work.

My question relates to connectors, and specifically what connector my Giant uses?

Apologies for the poor focus...
This is the connector on my Giant charger - it doesn't look anything like an XT60 or Rosenberger or XLR...

Are connectors available to connect say the Satiator or Luna charges to my Giant?

cheers
Mike

 

[Stefan Mikes]

Mike: Proprietary batteries require proprietary chargers. Giant Smart Charger is more than something you could use for DIY solutions. You certainly don't want a fire you could not extinguish. (Also, I would follow manufacturer's guidelines were I you).

 

[almikel]

Hi @Stefan Mikes ,

I respectfully disagree - battery chemistry is not complicated, nor are e-bike battery monitoring systems (BMS), and using a charger that is designed to charge to 80% max voltage will prolong the life of my battery, and certainly not increase the risk of fire.
I'm not talking DIY, just a connector that would enable connecting a highly regarded charger such as the Satiator to my Giant.

Also, I would follow manufacturer's guidelines were I you

Do you mean discharging the battery fully every 3 months?
This is stated in the Giant manual and was recommended to me by the LBS.
Based on my research of Li-ion battery chemistry it's no longer required - it's "old school" thinking based on older generations of battery chemistry (eg NiCad - which had a "memory" effect)

I'm completely fine to disregard some aspects of what Giant says in their manual and what the LBS says regarding battery care/longevity as long as the reasons I disregard their guidance are based on good science.

cheers
Mike

 

[Stefan Mikes]

I'm not talking DIY, just a connector that would enable connecting a highly regarded charger such as the Satiator to my Giant.

You have been warned.

 

[Lightning P38]

Thanks for your reply Ravi. From what I can tell by many of the commenters in this forum, your opinion can be trusted a lot more than what the BMS on my bike is telling me! I will try to put the battery through a couple of deep cycles before winter and see if that assists in giving more accurate SOC readings, but my hopes are not high, and I am not prepared to shell out more cash at this point for more sophisticated equipment.

The other thing I have noticed on my soc display, is when I am pulling a hill and drawing a lot of power the soc drops lower than it really is, and after the hill and/or I drop the e-assist level, the soc display will come back up to where it really is. In other words, a brief rest for the battery allows it to recover and is reflected in the soc display. One of those things you get used to seeing on your soc display.

 

[Two is Better than Four]

I finished my ride with 16% left on battery. Next morning it reads 22% when I start up. I realize that batteries fluctuate and a rest will up the percentage. My question is what percent should I read or go by just before charging back up - is it the percent I see at the end of my ride?
Thanks!

 

[Lightning P38]

I finished my ride with 16% left on battery. Next morning it reads 22% when I start up. I realize that batteries fluctuate and a rest will up the percentage. My question is what percent should I read or go by just before charging back up - is it the percent I see at the end of my ride?
Thanks!

You can do either, as I round to nearest 20% anyway to estimate charge time. As my display drops in 20% increments, when I am using the battery. If I want more precision, I can use my digital volt meter and measure the soc via voltage level.
I always power up the display to see the percentage charge before I plug in the charger, so I can estimate charge time.

I used to use a digital volt meter to check the voltage to determine the charge state, but then I got a feel for the display levels and the needed time to recharge, so I don’t bother with that.

 

[almikel]

On My Giant Bike the App tells me more precisely what % Level I am currently at.

So I figured out a Formula to "Time" the % Needed.
(for my battery & charger)

It is as follows:

2.25 Minutes for every % of charge needed.

Example:
If Battery is currently at 32%
But I want it at 80%
Take 80% minus 32% and it Equals 48
48 X 2.25 minutes = 108 minutes
That is 1 hour & 48 minutes Charge Time

This formula gets me within just a couple percentage points every time....................

HOW AM I DOIN RAVI ?

I've been convinced by members here with much more experience than I do to not muck with aftermarket chargers for my Giant...so I'll likely purchase another OEM Giant charger to use at work for days where I deplete the battery too far on a morning ride to get home in the afternoon.
I really like the idea of @CSH's post above for calculating the approx time of charging, and had some questions on the maths and the Giant specs for my battery (Giant Revolt with a 375Wh, 36V battery)

• Giant quote 375Wh, 36V, 13.8Ah for my Revolt (https://www.giant-bicycles.com/au/revolt-eplus-pro-2020 ) - but 36V x 13.8Ah = 497Wh, so either the battery is > 375Wh or the 13.8Ah is more like 10.5Ah - I'm assuming the latter (375Wh and 10.5Ah) - can anyone comment? I'm guessing Giant just incorrectly quoted the Ah rating from one of their 500Wh bikes (or Marketing just getting funky/enthusiastic) ??
• the Giant EnergyPak smart charger is quoted at 6A, which seems a lot to be dumping into a 10.5Ah battery - just under 0.6C - whereas if the battery was a 500Wh 13.8Ah, the 6A charger would only be charging at 0.43C (I realise the Giant charger is "smart" and will back off the amps when getting above 80%) - is charging a 10.5Ah battery at 6A (0.57C) too fast, or remains fine as long as I let the battery cool after a ride prior to charging and monitor temperature during charging?

Back to some maths - I'm keen to come up with some numbers to approximate charging times similar to what @CSH did above.
My battery is 375Wh 36V, and the Giant specs on the charger claim 6A current - which is a lot - next time I'm charging I'll take note to feel how hot the DC.
I'm assuming the Giant smart charger charges at 42V, and up to around 80% battery capacity should be supplying up to 6A to the battery.

• 6A x 42V = 252W - ie what the charger is delivering assuming full current (6A)
• 375Wh/252W = ~1.5hours to full charge (ignoring that the "smart" charger will back off the current once the battery hits ~80% or so) - this seems too quick - have I got my maths wrong?
• assuming the above is correct 90 minutes for 100% is 0.9 minutes for 1% or 54s for each 1% - which again looks way to short compared to @CSH 's calc above of 2.25min of each % charged - have I got my maths wrong?

@CSH if I backwards engineer your numbers of 2.52min for every 1% of charge increase, that's 252min or 4.2h to fully charge (100%) - which "feels" about the right amount of time to fully charge a depleted battery - but it obviously depends on the battery size (Ah), voltage, and charger current.
If I assume (maybe incorrectly) your Giant has a 36V battery and the same smart charger as I have (charging at 42V and 6A max and ignoring "smart" charger reduction in current at the top end), my maths again appears way out:
42V x 6A = 252W
252W x 4.2Hours = 1058 Wh - and I'm assuming the battery on your Giant isn't 1KWh

Somewhere along the line I've got the maths wrong...but I don't know where ?

cheers
Mike

 

[Stefan Mikes]

I'm guessing Giant just incorrectly quoted the Ah rating from one of their 500Wh bikes

This.

Giant Smart charger is smart. It means it "talks" to given battery and adjusts necessary charging current. It is not necessarily 6 A at all times. I own Giant 500 and 625 Wh batteries: No issue on charging ever. In my opinion, the charger is even too smart. Assume you have discharged your battery from 100 to 96%. An attempt to recharge to 100% will fail. The charger actually assumes it is OK to start charging at some 92% state of charge.

 

[almikel]

I'm guessing Giant just incorrectly quoted the Ah rating from one of their 500Wh bikes

This.

Cheers Stefan - I'm ok to call it a typo/lazy editing instead of Giant's marketing department getting "creative".

Part of the reason my Giant Revolt weighs < 20kg is because it only has a 375Wh battery - which I'm very happy with, as it suits my riding perfectly.

In my opinion, the charger is even too smart. Assume you have discharged your battery from 100 to 96%. An attempt to recharge to 100% will fail. The charger actually assumes it is OK to start charging at some 92% state of charge.

I'm OK with that level of "smart"

It means it "talks" to given battery and adjusts necessary charging current

It was this "feature" that convinced me to give up on using aftermarket chargers for my Giant - ie the proprietary interaction between the Giant BMS/battery and the Giant smart charger.
I've rationalised this as acceptable, but hence I'm stuck with using timers if I choose to have a max charge around 80% to prolong battery life...
...and I get that batteries are part of "consumable items" on an e-bike...I just want to do what I can to make my batteries last.

Mike

 

[Xyeet]

Any charger recommendations for 48V 24Ah battery in Hailong casing and 3 XLR connector? I'd like something smart that I can change to charge only to 80% or 90%. Is there cheaper alternatives than those in original post?

 

[Gionnirocket]

If you are relatively handy and understand basic electricity you can make this unit as I have to work with any charger.
I can charge to any voltage and it has worked well without issue.
DIY Smart Charger