# Buying a 2nd battery



## jann71 (17 Dec 2019)

I've considering buying a 2nd battery to use on some longer full day/weekend rides/touring where I may not have the option to charge the battery.

The current battery is Bosch 400 power pack.
Cheapest I can find a new 400 is about £420 or more if I go for a 500.

Any advice (apart from buying a 2nd ebike) on buying 2nd hand? There are few on eBay.


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## Pale Rider (17 Dec 2019)

Bosch batteries have a longer service life than some of the cheaper 'no brand' Chinese batteries, but buying second hand is still a risk.

£420 is a good price for a new 400, although you can never have too much capacity so I would consider lashing out on a 500.


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## ColinJ (18 Dec 2019)

Pale Rider said:


> Bosch batteries have a longer service life than some of the cheaper 'no brand' Chinese batteries, but buying second hand is still a risk.


I bought a cheap 'no brand' replacement battery for my laptop. It only took about a year to lose 50% of its capacity!


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## Pale Rider (18 Dec 2019)

ColinJ said:


> I bought a cheap 'no brand' replacement battery for my laptop. It only took about a year to lose 50% of its capacity!



Use, as in current draw, plays a part.

One of the reasons the Bosch batteries last a long time is the system is set very conservatively, so it doesn't thrash the battery.

I've seen several laptops at work with knackered batteries.

My guess is laptops from the 90s and 2000s thrashed the batteries with high current draw to achieve a working life of a few hours.

Lots of laptops these days will run all day, yet I don't hear of so many knackered batteries.

Battery technology will have improved a little, and I suspect modern laptops need less power to run.


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## ColinJ (18 Dec 2019)

Pale Rider said:


> Use, as in current draw, plays a part.
> 
> One of the reasons the Bosch batteries last a long time is the system is set very conservatively, so it doesn't thrash the battery.
> 
> ...


The new laptop that I am using today doesn't have a removable battery so I hope that the battery lasts at least 5 or 6 years! (It is still ok after 2.5 years.) Its LED backlight possibly uses less power than the fluorescent tube in my old laptop. The processor can cut its power consumption right down when running undemanding applications, but ramp up when more oomph is needed - a bit like the motors on your e-bikes. When the browser was idling, the battery power display estimated 6 hours remaining run time. Now that I am actually doing something, it has cut that to 4 hours. If I run something more power-hungry and/or turn up the screen brightness then that can fall to 3 hours.

I bought an Android tablet back in 2012 and that still has a decent battery life. I use that for 30 - 90 minutes every day. A couple of years ago I looked up how to take the thing to pieces to solder in a new battery but that has not been necessary. 

OTOH, I have had phone batteries die after a couple of years. Those have all been removable ones. The battery in the phone that I use now is soldered in so I will probably just replace the phone if/when that goes. (That is probably what manufacturers want - provide enough life so that people don't feel angry when the batteries finally die, and then sell them new kit!)


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## Mark pallister (18 Dec 2019)

jann71 said:


> I've considering buying a 2nd battery to use on some longer full day/weekend rides/touring where I may not have the option to charge the battery.
> 
> The current battery is Bosch 400 power pack.
> Cheapest I can find a new 400 is about £420 or more if I go for a 500.
> ...


Someone has a nearly new one for sale on adrians bike community


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## Blue Hills (18 Dec 2019)

Mark pallister said:


> Someone has a nearly new one for sale on adrians bike community


How can you judge how new it might be/how much use it has had?


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## Mark pallister (18 Dec 2019)

Blue Hills said:


> How can you judge how new it might be/how much use it has had?


I think you can find out how many charges it’s had and hours used as you can with a phone
i think the newer type head units display this info


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## Pale Rider (18 Dec 2019)

A Bosch dealer with the appropriate software can interrogate the battery to get its condition and pattern of use.

Not practical when buying used, unless the seller is offering the battery with a printout as proof of provenance.


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## Mark pallister (18 Dec 2019)

Pale Rider said:


> A Bosch dealer with the appropriate software can interrogate the battery to get its condition and pattern of use.
> 
> Not practical when buying used, unless the seller is offering the battery with a printout as proof of provenance.


Pay your money you take your chance then


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## rualexander (18 Dec 2019)

Is there any adapter system to charge a proprietary branded battery from a more generic or budget battery?


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## Pale Rider (18 Dec 2019)

rualexander said:


> Is there any adapter system to charge a proprietary branded battery from a more generic or budget battery?



The Bosch system is known to be locked down - think of it as the Apple of ebikes.

No pattern batteries are available for the latest battery shapes, although there were some for the previous shape battery which was discontinued in 2014.

The OP has a newer bike, so it's Bosch branded batteries only.


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## rualexander (18 Dec 2019)

Pale Rider said:


> The Bosch system is known to be locked down - think of it as the Apple of ebikes.
> 
> No pattern batteries are available for the latest battery shapes, although there were some for the previous shape battery which was discontinued in 2014.
> 
> The OP has a newer bike, so it's Bosch branded batteries only.



Yeah but if you had a cheaper generic/budget battery that could output the same voltage/current as the Bosch (in this case) charger and a suitable connector then presumably it could be done, unless the Bosch charger communicates with the battery?
Or maybe an inverter between the budget battery and the Bosch charger and battery would work, although that would no doubt be inefficient.


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## Mike_P (18 Dec 2019)

Bit off thread but why is there no dynamo charging system for ebike batteries topping it up as you ride?


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## neil_merseyside (18 Dec 2019)

Mike_P said:


> Bit off thread but why is there no dynamo charging system for ebike batteries topping it up as you ride?


Perpetual motion like that was outlawed by the energy companies.


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## Pale Rider (18 Dec 2019)

rualexander said:


> Yeah but if you had a cheaper generic/budget battery that could output the same voltage/current as the Bosch (in this case) charger and a suitable connector then presumably it could be done, unless the Bosch charger communicates with the battery?
> Or maybe an inverter between the budget battery and the Bosch charger and battery would work, although that would no doubt be inefficient.



There's no way of connecting a budget battery to the bike.


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## rualexander (18 Dec 2019)

Pale Rider said:


> There's no way of connecting a budget battery to the bike.


I'm not talking about connecting a budget battery to the bike.
I meant some way of using a budget battery to recharge an official branded battery.


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## ColinJ (18 Dec 2019)

neil_merseyside said:


> Perpetual motion like that was outlawed by the energy companies.


You could use (say) 25 W of spare leg power to do it on the flat for long periods of time and get that back for short boosts on climbs. You could also use the generator as a brake rather than converting all your kinetic energy into heat when stopping.


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## Pale Rider (18 Dec 2019)

rualexander said:


> I'm not talking about connecting a budget battery to the bike.
> I meant some way of using a budget battery to recharge an official branded battery.



Even if you could connect the two batteries together, there's still no way of transferring the charge instantly.

The OP wants to flatten battery number one, stop for a few seconds to instal battery number two, them continue.



ColinJ said:


> You could use (say) 25 W of spare leg power to do it on the flat for long periods of time and get that back for short boosts on climbs. You could also use the generator as a brake rather than converting all your kinetic energy into heat when stopping.



It takes several hours at mains (rectified) current to charge the battery.

The amount of charge you could recover by taking a small amount of leg power and while braking is miniscule.

The inefficiency of the charging process also works against you, it takes more power to recharge a battery than the battery is able to harvest.

Look at it like a bike dynamo.

For a small amount of resistance it's possible to run an LED bulb or two.

To produce enough charge to meaningfully charge a battery would make the bike feel like it was permanently on a steep gradient, which rather defeats the object.


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## rualexander (19 Dec 2019)

Pale Rider said:


> Even if you could connect the two batteries together, there's still no way of transferring the charge instantly.
> 
> The OP wants to flatten battery number one, stop for a few seconds to instal battery number two, them continue.



Ah ok, I thought it was for touring overnight where the battery could be recharged after the day's riding. For example in wild camping situations, to extend range between places with mains electricity.


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## Mark pallister (19 Dec 2019)

Mike_P said:


> Bit off thread but why is there no dynamo charging system for ebike batteries topping it up as you ride?


First company that cracks that one will be 💰💰
I bet there’s plenty working on it now


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## CXRAndy (19 Dec 2019)

E-bike batteries are 36 Volts or more, dynamo are 6 Volts usually. You could have one wound to produce a higher voltage output. The drag producing more voltage and current is not worth the small amount of current to top up the e-bike battery. You're better off buying a bigger battery at the start. 

That's why I never did favour the proprietary systems like Bosch, who lock down the whole system. 

I went with open software with customised settings of voltage,current and power. I run a 52V battery on a 48V setup


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## Smudge (19 Dec 2019)

When out & about on my ebikes, the most often asked question is 'Does it charge while you ride it ?'
I've got so bored of trying to explain the physics of how that wouldn't work, that now i just say 'Yes it does, it has a perpetual motion setting'. I then point to some random button on the display.
They nod and smile knowingly and i can get on with wherever i'm going.


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## classic33 (19 Dec 2019)

https://www.treehugger.com/bikes/li...itself-while-you-ride-it-unlimited-range.html


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## Smudge (19 Dec 2019)

classic33 said:


> https://www.treehugger.com/bikes/li...itself-while-you-ride-it-unlimited-range.html



Having regeneration systems on ebikes, is nothing new. Its been tried before. But they just haven't worked with any success.
Maybe someone will crack it one day, but i'm not going to automatically believe the claims of a company trying to flog their new ebike.


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## CXRAndy (19 Dec 2019)

classic33 said:


> https://www.treehugger.com/bikes/li...itself-while-you-ride-it-unlimited-range.html





Smudge said:


> Having regeneration systems on ebikes, is nothing new. Its been tried before. But they just haven't worked with any success.
> Maybe someone will crack it one day, but i'm not going to automatically believe the claims of a company trying to flog their new ebike.



Technically it is correct, whilst ignoring the regen power is derived mostly from human effort


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## Smudge (19 Dec 2019)

CXRAndy said:


> Technically it is correct, whilst ignoring the regen power is derived mostly from human effort



Exactly, you dont get power from nothing. A force has to produce that charging power, and that force would have to come from the rider where ebikes are concerned.
The trick would be developing a small lightweight dynamo, that produces hardly any drag but outputs a lot of charging power. If this holy grail existed, it would already be available.


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## classic33 (19 Dec 2019)

CXRAndy said:


> Technically it is correct, whilst ignoring the regen power is derived mostly from human effort


I never said it was free.


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## ebikeerwidnes (19 Dec 2019)

I saw an electrical engineer commenting that they can make an efficient motor and they can make an efficient generator

what they can;t do is make an efficient motor that will also act as an efficient generator when required
and clearly adding an extra piece of machinery has weight penalties which would be annoying


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## ColinJ (19 Dec 2019)

ebikeerwidnes said:


> I saw an electrical engineer commenting that they can make an efficient motor and they can make an efficient generator
> 
> what they can;t do is make an efficient motor that will also act as an efficient generator when required
> and clearly adding an extra piece of machinery has weight penalties which would be annoying


The Cruachan pump storage power station at Loch Awe does pretty well! They reckon it is at least 70-80% efficient and maybe better than that.


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## ebikeerwidnes (19 Dec 2019)

Thanks - interesting
but I wonder if it is that easy for smaller systems
and also - how much heavier would it make it??

also - if it is 70-80% efficient - would that mean a 20-30% reduction in range??

any electrical experts out there know better than me - which ain't difficult


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## neil_merseyside (19 Dec 2019)

ColinJ said:


> The Cruachan pump storage power station at Loch Awe does pretty well! They reckon it is at least 70-80% efficient and maybe better than that.


Erm no:-
From Wiki
"Cruachan is not a net generator of electricity: it uses more energy for pumping water and spinning its turbines than it generates "
I suppose you could nip onto Wiki and change that if you wanted... but it's just a pumped storage power station. 
All it does is use cheap rate power (maybe wind/solar oversupply?) to fill the top reservoir to be released it when needed. 
It's a water charged battery of sorts.


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## ColinJ (19 Dec 2019)

neil_merseyside said:


> Erm no:-
> From Wiki
> "Cruachan is not a net generator of electricity: it uses more energy for pumping water and spinning its turbines than it generates "
> I suppose you could nip onto Wiki and change that if you wanted... but it's just a pumped storage power station.
> ...


Erm _*yes*_!

I was pointing out (as a former electrical engineer!) that a pump (effectively a type of motor) _can _be a very efficient generator, which goes against what you posted earlier. I wasn't talking about a perpetual motion machine which magics energy up from nowhere.



ebikeerwidnes said:


> if it is 70-80% efficient - would that mean a 20-30% reduction in range??


You would only use it for recharging the battery and the capacity of that wouldn't change. It means that you could in theory get back a useful amount of energy coming down a big hill, for instance. I did a quick calculation (which may be wrong!) and I think you could get back about 60 Wh of energy going down a steep 200 m descent using motor-generator as a brake. (That is assuming 120 kg of rider and bike and about 75% efficiency.)

You could cycle along on the flat charging the battery instead of using the battery to operate the motor. As Pale Rider pointed out though it would be hard work if you had it set up to generate a lot of power and you don't buy an e-bike to make cycling harder!


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## confusedcyclist (20 Dec 2019)

Pale Rider said:


> Battery technology will have improved a little, and I suspect modern laptops need less power to run.


My 2014 mac air only uses ~20 watts when idle which blows my mind, because my desktop varies from 250-600 depending on if it's idle or running an intense application, and that's before you factor in my display, which of course is integrated into the Mac.


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## classic33 (20 Dec 2019)

The everlasting battery.


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## confusedcyclist (20 Dec 2019)

Mike_P said:


> Bit off thread but why is there no dynamo charging system for ebike batteries topping it up as you ride?


You can do it, and in some circumstances it may make some sense, like retrofitting to a bike which can't be setup with integrated lighting for whatever reason. Purpose built ebikes supplied with lighting as standard will always utilise a direct feed from the battery because the drag and conversion losses caused by the dynamo light and hub combo would waste more energy than a direct feed from the battery to a lamp. As a rule of thumb, whenever you convert energy from one form to another you lose energy, usually through heat, light and sound, the rate of loss is known as efficiency. This is why light bulbs get hot and sometimes buzz, even though we usually only want them to produce light.

Lets assume for the sake of simplicity that the rate of loss is 20% at each stage of conversion, and we need 3 watts to power the lamp, you're going to need to supply more watts from the battery to ensure 3 watts makes it to the lamp after all conversion losses, with 5 steps of conversion (Battery - Elec - Kinetic - Elec - Light), you're going to need to supply 10 times as many watts from the battery. I'm not an electrical engineer and I'm not 100% sure on the actual loss %, it does vary at each stage. But that's in essence the reason you won't see dynamos on commercial ebike systems.

Of course, 30 watts is negligible on a 250w motor, you can expect the rider to put in another 100w easily, so you're looking at less than 1% of overall power, but still that is lost range on an ebike. I would not fit a dynamo hub to an ebike personally, it would make more sense for my kind of riding to fit removable battery powered lights and preserve the range and long term wear on the expensive bike battery. Charging the LED lights from my bike is still possible, as I can hook up 1 2AMP USB device to my Bosch Kiox Display, so I could charge in a bind.


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## confusedcyclist (20 Dec 2019)

ColinJ said:


> ...using motor-generator as a brake.


The problem with regenerative braking is a person on a bike weighs a lot less than a car. Therefore there is a lot less energy available to be captured (which is what regenerative braking does). When you cycle, about 90% of your effort and energy goes into pushing you through the air which resists you as you move. Perhaps less than 10% is lost because you brake – so even in the best case scenario when you capture all of your kinetic energy when you brake, you’ll only go 10% further as a result. Of course, we haven't even started to factor in conversion losses or weight and costs of such a system.


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## ColinJ (20 Dec 2019)

confusedcyclist said:


> The problem with regenerative braking is a person on a bike weighs a lot less than a car. Therefore there is a lot less energy available to be captured (which is what regenerative braking does). When you cycle, about 90% of your effort and energy goes into pushing you through the air which resists you as you move. Perhaps less than 10% is lost because you brake – so even in the best case scenario when you capture all of your kinetic energy when you brake, you’ll only go 10% further as a result. Of course, we haven't even started to factor in conversion losses or weight and costs of such a system.


Yes, I'm sure if it were worth doing then somebody would already be doing it and making a big deal about it!

One day somebody very clever will come up with new battery technology which will make it possible to ride all day on one charge using a battery which doesn't weigh much and doesn't cost much either. Some interesting new technologies are mentioned in THIS ARTICLE.


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## confusedcyclist (20 Dec 2019)

ColinJ said:


> Yes, I'm sure if it were worth doing then somebody would already be doing it and making a big deal about it!
> 
> One day somebody very clever will come up with new battery technology which will make it possible to ride all day on one charge using a battery which doesn't weigh much and doesn't cost much either. Some interesting new technologies are mentioned in THIS ARTICLE.


Its an exciting field, never say never as they say. We have been working on batteries for 200 years and we have only increased performance 5x in that period. I temper my own enthusiasm and don't expect quite so dramatic gains as you propose. We are close to limits of energy density that can be achieved with commercialised liquid battery chemistry. Much needed improvements at this stage would be to switch from rare earth minerals which are about to peak and become much more expensive, or improve recyclability, both of which are show stoppers as far as affordable batteries and green credentials go.


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## CXRAndy (20 Dec 2019)

We need the flux capacitor


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## classic33 (20 Dec 2019)

confusedcyclist said:


> Its an exciting field, never say never as they say. *We have been working on batteries for 200 years and we have only increased performance 5x in that period.* I temper my own enthusiasm and don't expect quite so dramatic gains as you propose. We are close to limits of energy density that can be achieved with commercialised liquid battery chemistry. Much needed improvements at this stage would be to switch from rare earth minerals which are about to peak and become much more expensive, or improve recyclability, both of which are show stoppers as far as affordable batteries and green credentials go.


_"Baghdad Battery?_


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## jann71 (22 Dec 2019)

I'm looking at a few used ones. Quite a jump from a 400 to 500.
Different serial numbers, different year?


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## Pale Rider (23 Dec 2019)

The passage of time will eventually kill any battery, but pattern of use has a bigger impact.

Buying used it's very hard to get accurate information on either of those two things.

I would be inclined to ask the owner how the battery has been used or how many miles it has done.

But ultimately buying a second hand battery is a risk you will have to take.


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## jann71 (23 Dec 2019)

They are saying it's brand new but without box. Offering return within 30 days.
So I'm thinking if buy it and take to dealer to plug in to check and if it's got any issues send it back.


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## Pale Rider (23 Dec 2019)

A full discharge test takes several hours/over night.

The dealer might charge anything up to £50, but you will get a print out giving details of use and condition, and a percentage efficiency figure.

That would be something to take to the seller if there was a problem.


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## jann71 (23 Dec 2019)

Thanks for your help Pale Rider.


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## jann71 (11 Jan 2020)

Just whacked the cost of a new 500wh on my credit card 😳


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