How to carry a 2nd / extra battery ...

Trod

Finding my (electric) wheels
Aug 11, 2021
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Just trying to do research on the best way to carry a 2nd / extra battery. If anyone is already doing this, please share how you do it and any advice you have ?
 

richtea99

Esteemed Pedelecer
May 8, 2020
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I suspect it depends on the battery width & length, but in a waterproof bag strapped under the top tube, or on a rack. Here's a posh example for a Fazua:

Crazy price.
 

guerney

Esteemed Pedelecer
Sep 7, 2021
1,297
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There's enough room on the pannier rack for me to carry two batteries side by side, if I bolt on a slab of alumiunium slightly wider than the pannier rack, and the battery mounts to that - but I haven't needed to try this yet.
 

Benjahmin

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Nov 10, 2014
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I have a soft case battery made by Jimmy. I have wrapped it in an extra layer of high density foam plastic and it sits in the bottom of one of my panniers.
I am careful to monitor it's physical condition, including the connection leads. I always measure both it's voltage and the rack battery voltage before connecting them together. Both important for health and well being of the battery and yourself/household.
It is extra weight but it's relatively low down and I'm not really aware of it. That said my riding is all tarmac, no acrobatics !
In combination it gives me a ridonculous nominal 28Ah, much needed in hilly W.Wales to aleviate range anxiety.
Also, using both at the same time, halves the current draw from each battery so stressing them less and, hopefully, extending their life.
The pannier is suffering weight stress, but it's been about 4 years now doing this and it is still going strong if damaged. (Axiom panniers).
 
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cyclebuddy

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Nov 2, 2016
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It depends which ebike I'm riding, but generally I'll carry a (bubble-wrapped) spare battery either within a normal backpack or in a trunk on the bike rack. Works fine. No special bags or carriers needed.
 

Andy-Mat

Esteemed Pedelecer
Oct 26, 2018
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I have a soft case battery made by Jimmy. I have wrapped it in an extra layer of high density foam plastic and it sits in the bottom of one of my panniers.
I am careful to monitor it's physical condition, including the connection leads. I always measure both it's voltage and the rack battery voltage before connecting them together. Both important for health and well being of the battery and yourself/household.
It is extra weight but it's relatively low down and I'm not really aware of it. That said my riding is all tarmac, no acrobatics !
In combination it gives me a ridonculous nominal 28Ah, much needed in hilly W.Wales to aleviate range anxiety.
Also, using both at the same time, halves the current draw from each battery so stressing them less and, hopefully, extending their life.
The pannier is suffering weight stress, but it's been about 4 years now doing this and it is still going strong if damaged. (Axiom panniers).
You obviously understand the pitfalls of such an arrangement very well. Really very well done.
I myself, with extensive electrical knowledge gained over almost 50 years, would have bought a special two channel BMS to handle the two batteries, coward that I am!!!
But I also like having the second battery, but disconnected in the pannier, not being used, so that if and when the first battery is too low, I can do a quick swap and have a fully charged replacement in place in less than a minute.
But anyone else here who is tempted to follow in your footsteps, please be careful before trying this out, as you REALLY need to understand and know what you are doing, as does Benjahmin obviously does.
Otherwise there could be a big bang and or fire.....something expensive possibly!! o_O:confused::mad:
regards
Andy
 

Tony1951

Pedelecer
Mar 27, 2016
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Yes - the warnings about fire caused by connecting un-alike batteries in parallel need to be clear to people. Even when some users made electronic provision to isolate the second battery to stop a flat one being surge charged by a good one, there have been failures. There was a video on here made by some New Yorker who had connected a new high capacity battery to his ebike in parallel with his old battery and the video showed a spectacular fire outside his apartment. This guy was blaming the 'Chinese' ' Cr@p' battery he had bought, but I think his battery isolation technique had let him down and that there was a massive flow of current from one battery to the other.

Carrying a spare battery and swapping them out is completely safe. That is what I would do if I needed extra range.
 

Andy-Mat

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Oct 26, 2018
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Yes - the warnings about fire caused by connecting un-alike batteries in parallel need to be clear to people. Even when some users made electronic provision to isolate the second battery to stop a flat one being surge charged by a good one, there have been failures. There was a video on here made by some New Yorker who had connected a new high capacity battery to his ebike in parallel with his old battery and the video showed a spectacular fire outside his apartment. This guy was blaming the 'Chinese' ' Cr@p' battery he had bought, but I think his battery isolation technique had let him down and that there was a massive flow of current from one battery to the other.

Carrying a spare battery and swapping them out is completely safe. That is what I would do if I needed extra range.
Good post.
Is that battery fire you mentioned on YouTube? Can you post a link for it if its on there please?
I like this one from Holland I believe, and you can see a new battery on the down tube, and the original one on the rack, which appears to have been pulled back from the socket before the video was started!
The only way to stop these batteries burning, is to completely immerse them in water and leave them there for quite a long time! Using a hose, as in the video, will usually prevent the fire spreading, but that is just about the limit, it won't stop burning.
German Police have large tanks available around Germany for when electric car batteries catch fire, and a small crane, so that they can place burning e-cars in the tank. Its quite a business. As some e-car Lithium batteries can burn for up to 12 hours if not cooled....

This one appears to "only" gas, but those fumes are poisonous!

Regards to all and please stay healthy
Andy
 

Nealh

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In one of Guy's programmes they deliberately set an e car on fire by remotely shorting the batteries, fire brigade tested a large fireproof type tarp to cover the whole car. And is more practical then hoisting a car in to a tan of water. As they demonstrated the flames extinguished due to no oxygen but the process of allowing the heat to cool was needed to prevent self ignition again.
 

Andy-Mat

Esteemed Pedelecer
Oct 26, 2018
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In one of Guy's programmes they deliberately set an e car on fire by remotely shorting the batteries, fire brigade tested a large fireproof type tarp to cover the whole car. And is more practical then hoisting a car in to a tan of water. As they demonstrated the flames extinguished due to no oxygen but the process of allowing the heat to cool was needed to prevent self ignition again.
I think its true to say that we all learn as we go along, methods change and get improved on, though such a Tarp is unlikely to strike a chord with most of the e-bike community I feel......speaking for myself of course, but I rarely "fiddle" with the insides of batteries, and know enough not to connect two together.....
But the making all of our fellow e-bikers fully aware of any possible danger is an important task that we need to always stay abreast of, as new members join, don't you think?
Andy
 

Nealh

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One suspects any fire from paralleling batteries is more down to mismatched SOC's rather then unequal capacities or batteries of differing voltage, a lot of current flows if the voltages aren't very close.
I have ran parallel's on my bikes for over 6 years now no issues at all.
My Swizzbee runs two 24v packs in parallel one 23.2ah and the other 17.5ah giving a max 220a rating. There have been the odd scare story but with no details to quantify them as to why they really went wrong or what bad practice may have been involved
 

StuartsProjects

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May 9, 2021
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I have two batteries too, 11Ahr and 17Ahr.

The eBike is a converted hardtail titanium mountain bike with a down tube mounted shark type battery.

To carry the second battery, when needed, I bought a rucsack which is big enough to carry the battery when its in a box made out of the 20mm packing foam that stuff like batteries gets delivered in. The foam provides some protection to the battery in the event of a crash.

However, I dont need to put the battery in the foam box since the rucksack has side pockets that are big enough to put a battery in. I took a battery to the local Go-Outdoors looking for a rucsack with suitable side pockets.

The rucsack will double up as a walking rucsack which it is big enough for, but its not so big that it gets in the way on a bike.
 

Flycaster

Pedelecer
Sep 29, 2019
26
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Sorry to hijack your thread but I have searched for days looking for a bag for the rear rack to fit a Woosh Gran Camino battery with no look. I don't know if the OP is looking how to use two batteries at once or if he is like me, just wants to transport another battery safely on a rack?
 

egroover

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Benjahmin

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The Do's and Dont's of paralleling batteries.
1 They MUST be the same specified voltage.
2 They MUST be charged seperately (i,e disconnected from each other). This can be with their own individual chargers or use the same charger consecutively.
3 You must always check that the state of charge (soc) voltage is equal BEFORE you connect them together - EVERY TIME.
A voltage difference of 0.1v is tolerable though not ideal. If one battery is higher than the other I generally finish the lower battery with the charger from the higher battery, this usually brings them in.
4 The connection lead, or Y lead, should have clearly marked connectors (mine are red and black) to avoid wrong polarity connection as this would be catastrophic. I use single pole Anderson Power plugs physically slotted together - difficult to reverse connect but not impossible so pay attention. Some sort of 2 pole irreversible plug and socket would be better, perhaps others can advise.
5 Ideally the batteries are the same capacity though not essentially, however I think they should be close as possible for best operation. Mine are both nominally rated at 14Ah. As they contain different cells and are of different ages, there will be a difference. I couldn't say how this would play out when running to near empty as that has never happened - that's why I've got two batteries :cool:.
6 If carried in a pannier or rucksack, the second battery must be physically protected. I take mine out of the pannier for every charge so that it gets a visual inspection. Pay attention to the charge and discharge leads.

I am a sparky by training and am aware that even low voltage batteries can be very 'lively' if mistreated. Just because 36v doesn't give you a discernable shock don't disrespect it. The current flow of wrongly connected D.C. can be immense and extremely damaging.
I was taught a mnemonic as a lad. IT'S THE VOLTS THAT JOLTS, IT'S THE MILS THAT KILLS.
In other words a body can withstand a high voltage shock BUT if there is a current flow of only 30mA (especially across the heart) this is the killer. This illustrates that it's current that does the damage. In practice, you are never going to feel a shock from a 24 or 36v battery, but the current from it can burn you and anything around, badly.
So be aware, stay alert and you'll stay alive.
 

Nealh

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For belt and braces connections use a schottky diode inline to prevent reverse current flow. XT connectors for me one simply can't connect up incorrectly once soldered right.
 

Flycaster

Pedelecer
Sep 29, 2019
26
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I've got this rack bag


It has a special compartment in it that unzips and you can slide in a spare Hailong-1 battery, with room for other stuff in the top half and the side pockets
Brilliant thank you, exactly what I was looking for, I take it it just velro's to the rear rack? is it sturdy?
 

slowcoach

Pedelecer
Dec 11, 2020
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I remember when I was attending evening class on electronics at the local tech college, the teacher told us keep one hand in your pocket when working with dc to avaoid the risk of a small current across the heart.

Carrying a second battery. on my old Ezee Sprint, I made a bracket to fit on the seat down tube to hold the battery. When the first ran out of power, it took only seconds to remove both batteries and swap them around.
 
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Andy-Mat

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Oct 26, 2018
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For belt and braces connections use a schottky diode inline to prevent reverse current flow. XT connectors for me one simply can't connect up incorrectly once soldered right.
A reasonably sorted quality high wattage resistor could allow the two batteries to achieve identical voltages, but restrict the current to a reasonably low value.
The problem lies in the very low internal resistance that some battery types have, which allows almost unrestricted high currents to flow, if the balancing is performed wrongly.
This is true of identical battery sizes, or even ones with different sizes, but the same nominal voltage.
As an easy example, for 2 x 36 volt batteries, a resistor of say 30 Ohms in say the plus connection between the two (or both in the negative connections, it does not matter), would keep the current max possible to a little over 1 amp.
Though generally, it would be much less, as the voltage difference would be much less in practice, as it is unlikely that say one battery is fully charged and the other fully discharged, which would give a voltage difference of around 12 volts, or slightly less!
So calculating the power, a resistor of around 50 watts could more than handle the power very easily, all simple Ohm's Law.
Its actually safer than using a diode, which could still allow high currents to flow under certain conditions of error. The resistor exerts the same value of resistance connected either way round!
I hope this was helpful.
Stay healthy.
Regards
Andy
 

Andy-Mat

Esteemed Pedelecer
Oct 26, 2018
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I remember when I was attending evening class on electronics at the local tech college, the teacher told us keep one hand in your pocket when working with dc to avaoid the risk of a small current across the heart.

Carrying a second battery. on my old Ezee Sprint, I made a bracket to fit on the seat down tube to hold the battery. When the first ran out of power, it took only seconds to remove both batteries and swap them around.
Contrary to what many believe, AC is far more dangerous than DC. But only the really good books actually state that.
Its about a factor of 3 difference, if you compare the size of the killing current of AC to DC. 50ma to 150ma.
See the following links:-
The following link shows the belief of many years ago that DC is more dangerous, its not! Worst case DC can be painful burns, but AC sets muscles in spasm, NOT allowing the person to get off it on their own.
Naturally there is danger in both to a person who has not been correctly trained!
I hope that this was helpful
Stay healthy
Andy