# Bosch battery power drop off as charge reduces ?



## Ridgeway (29 Mar 2020)

Does anybody know if a decent battery and drive system (Bosch Active Line in our case) with a standard 400w battery would reduce it's pulling power as the battery charge reduces ? I assumed that the amount of assistance it provided would be pretty much equal throughout its charge. My wife who actually rides the bike suggest that it does drop off quite a bit which i was surprised about, then again she did say that it could just be her that was getting tired legs...

Battery has done about 3,000km so far and is 2yrs old, the range it shows and gives is still pretty much as new, perhaps about 15% down from it's original performance.

Thanks


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## Pale Rider (30 Mar 2020)

Reduced power delivery as the battery discharges is known as 'sag'.

All batteries do it.

Bosch tend to be better than some others, particularly batteries found on 'no name' cheap ebikes.

Battery management plays a part.

The Bosch system is set up to place moderate load on the battery, which means it may appear to sag less than a system with high current draw.

This also reduces wear on the battery which is why you've noticed the range to still be 'pretty much as new'.


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## Ridgeway (30 Mar 2020)

OK this makes sense and thanks for the comprehensive answer. It also backs up what you say about cheap non-branded e-bikes as we had one originally and the power dropped off on that something shocking however on the Bosch i personally hadn't noticed it although Mrs Ridgeway had and it's her bike that she uses 5 days a week.

Hopefully we can still get another 2-3k KM out of the battery before it needs replacing.

Thanks


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## Pale Rider (30 Mar 2020)

Ridgeway said:


> Hopefully we can still get another 2-3k KM out of the battery before it needs replacing.



Very likely you will, and a fair bit more.

My oldest Bosch battery is 2010, and while I don't now do a lot of miles on the ebike it's attached to, it's done 5,000+ miles and is still giving a reasonable range.

Battery longevity is also affected by rate of use, to get the best out of them they need to be used regularly, but thrashing the battery when you do use it will shorten its life.

Sounds like your partner's use is pretty much ideal to achieve a long life.


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## CXRAndy (3 Apr 2020)

Having a higher battery voltage helps with sag /performance drop off. They still do it though.

A benefit of open firmware


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## Levo-Lon (4 Apr 2020)

Can't say I noticed it on the trek , after 3yrs of use.
I used it a lot for 14 mile a day commute.
It was my wife's bike before I used it,and that was used for MTB 2015 model bought in late 2016.
3 days and re-charge ,I did have a good bit left in the battery as I used eco mainly and often kept above 15.5mph, flat lands smart Sam tyres.

To be honest buying a new battery after a few yrs is a factor but if it's replacing car ,bus, taxi ect it's got to be a minor consideration.

I think my Bosch battery would do 5 yrs plus no problem, my friend bought the bike so I'm sure she'll tell me when it fails


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## Legomutton (24 Sep 2021)

Other things being equal, the power will drop as the battery voltage falls, which they all do more or less when they discharge - measuring voltage is a common way of reporting state of charge.

The importance of this would depend for me on how marked it is. It will get gradually worse as the battery ages and its capacity reduces. The best defence is probably spare capacity, i.e. a battery with capacity that is materially higher than you need. 

I gave up trying to work out the best usage/charging practice, there's too much conflicting advice, you can't be sure what the BMS is doing on your behalf, and there's 'balancing' of cells in the equation somewhere. Now I just charge them when I get home if they are showing 3/5 lights or fewer. Leaving them well discharged is definitely bad because they could go completely flat through self-discharge, which will cause them to lose their virtue and in some cases they will remain effectively dead.


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## Scaleyback (24 Sep 2021)

Legomutton said:


> I gave up trying to work out the best usage/charging practice, there's too much conflicting advice,



'Conflicting advice' ? I understand it's pretty much accepted that lithium-ion batteries in ebikes and electric cars ( for longevity) are best used in the range approximately between 20 and 80%. Fully charging these batteries 'stresses' them and degrades them quicker. Exactly how quickly full charging degrades the battery seems to be a bit of a mystery. When charging them to 100% (for max range) it's best to complete this just prior to the ride. You probably know this ? but If rated for 1,000 charge cycles, this equates to a full charge. Equivalent to 2,000 50% charges, 4,000 25% charges etc etc.


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## Biker man (25 Sep 2021)

Pale Rider said:


> Very likely you will, and a fair bit more.
> 
> My oldest Bosch battery is 2010, and while I don't now do a lot of miles on the ebike it's attached to, it's done 5,000+ miles and is still giving a reasonable range.
> My battery has done 12000 miles very little sag .
> ...


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