Thread: Adding an extra battery pack to an electric scooter

14 NCR18650Bs in series will get you 52V and about 48 Ahr.

I wouldn't muck about with knockoffs and use LG or Panasonics or similar.

With this many batteries, unless you know what you are doing its pretty easy to damage the motor or even start a fire so I won't provide any further advice about connections/wiring etc over the web and it's best if you get someone local to .

there are many battery places that will build up packs to your specifications using 18650's... it's no longer a must-be-done-at-home enthusiast task

Originally Posted by BobL

14 NCR18650Bs in series will get you 52V and about 48 Ahr.

That would cost around $180-200 but I see these already built battery packs for example on Aliexpress have "many" more batteries hence their price is around $650-700.
Maybe they use a combination of in series and parallel so they use more batteries?

With this many batteries, unless you know what you are doing its pretty easy to damage the motor or even start a fire so I won't provide any further advice about connections/wiring etc over the web and it's best if you get someone local to .

I know people do it,I even watched a Youtube video made from a retailer in Singapore where Australians buy scooters.
But like I said I'm not an expert so that is why I need someone who knows the good stuff.

It's rare for Bob and I to disagree on electrical matters, but I just checked my online references and find 18650B cells to be rated at 3.4 AH. Fourteen cells in series will be in the region of 52V and 3.4 AH, not sure where Bob came up with 48 AH, even allowing for the possibility of a misplaced or missing decimal point. Closest I can see would be 14 cells in parallel giving around 48AH or 14 cells in series giving 52V, so would require and array of 14 p x 14 s to achieve 52V at 48AH, i.e 196 cells.

You will find that there are various brands and grades of cells available, and while there can be cost savings attributable to assemblers buying cells in bulk compared to end users buying them in small quantities, most of the savings offered by Asian suppliers at the cheap end of the price range are attributable to one of two things, either buying lower grade cells or not attempting to match cells prior to assembly.

Cell matching is a process where each cell is charged and discharged a number of times to test it actual capacity and sorted by capacity, then packs are assembled using only cells of similar capacity. This results in longer pack cycle life and greater energy recovery from the pack. Any pack is limited to the performance of the weakest cell in it, once that cell is effectively discharged, there may be considerable energy in the other cells, but extracting it for use runs the risk of causing permanent damage to the weak cell, causing it to be discharged progressively earlier on each subsequent charge/discharge cycle.

High quality packs use closely matched premium cells whereas bargain basement packs use random arrays of cells that are probably at the lower end of the the performance range to begin with.

For you extended range requirements, it may be better to attempt to arrange for recharge capability at the destination so you begin the return journey with a full charge if time permits a decent charge to be implanted in the pack.

Originally Posted by malb

For you extended range requirements, it may be better to attempt to arrange for recharge capability at the destination so you begin the return journey with a full charge if time permits a decent charge to be implanted in the pack.

Right now it takes 13 hours to recharge from 25-30% battery charge to 95% charge.
And I would be ok with an additional smaller external battery pack like 20-25Ah but the problem is that I don't know how to do it.
Will the BMS be able to manage both battery packs? Will the supplied charger be able to recharge both batteries?
These are some of the questions that only a capable person can deal with.

You should be able to charge the current pack faster than 2A, 30AH capacity at a 2A rate would be a minimum 15hrs, so what you are experiencing is what I am expecting. No battery pack will return 100% of the energy put into it by charging, so you always need to supply more than their rated capacity if they are flat. Lithium tend to have a better return efficincy than other chemistries, but are also more sensitive to overcharging and over discharging, hence the need for a BMS to control the charging and discharging.

Typically a lithium BMS system will monitor the pack voltage and disconnect the charger if the pack voltage exceeds a threshold, disconnect the load if the voltage falls below a given level, and also monitor each set of cells in a series/parallel array to bypass charge current for a parallel set of cells if the voltage of the set approaches the safe limit for the cell type, indicating that this particular parallel string is fully charged.

An additional battery pack would require it's own BMS to be incorporated into the pack, the original batteries BMS won't be able to access individual cells in the additional pack to offer charge bypass without modifying the original pack, and may not have the capacity to be able to bypass charge current for individual cells in both packs simultaneously.

The original charger could in theory charge both battery packs simultaneously, but it would take twice as long to supply twice as much energy. Without knowing the details of the original pack and it's BMS, I would not suggest investing in a higher current charger for the original battery, or for a combination of original and additional battery. The issue there is that the BMS needs to be able to bypass the charge current around a group of cells once it determines that they are at the charge voltage threshold, but may have current limits below the upgraded chargers capacity and may continue to charge the cells, creating a dangerous over voltage situation that can start a fire in the packs.

Ultimately my recommendation would be to acquire a battery pack and charger that match the original, charge them separately, and connect the second pack when the first is exhausted. This way you have range extension but no reduction in the safety engineered into the original pack.

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Originally Posted by malb

Typically a lithium BMS system will monitor the pack voltage and disconnect the charger if the pack voltage exceeds a threshold, disconnect the load if the voltage falls below a given level, and also monitor each set of cells in a series/parallel array to bypass charge current for a parallel set of cells if the voltage of the set approaches the safe limit for the cell type, indicating that this particular parallel string is fully charged.

The manufacturer recommends to not overcharge the batteries even so I suppose the system is configured with a BMS, maybe they just give generic recommendations in order to reduce under warranty returns.

An additional battery pack would require it's own BMS to be incorporated into the pack, the original batteries BMS won't be able to access individual cells in the additional pack to offer charge bypass without modifying the original pack, and may not have the capacity to be able to bypass charge current for individual cells in both packs simultaneously.

This information is also useful.

The original charger could in theory charge both battery packs simultaneously, but it would take twice as long to supply twice as much energy. Without knowing the details of the original pack and it's BMS, I would not suggest investing in a higher current charger for the original battery, or for a combination of original and additional battery. The issue there is that the BMS needs to be able to bypass the charge current around a group of cells once it determines that they are at the charge voltage threshold, but may have current limits below the upgraded chargers capacity and may continue to charge the cells, creating a dangerous over voltage situation that can start a fire in the packs.
Ultimately my recommendation would be to acquire a battery pack and charger that match the original, charge them separately, and connect the second pack when the first is exhausted. This way you have range extension but no reduction in the safety engineered into the original pack.

I agree this is the best safe and practical solution, I carry the second battery pack as a back up and only connect it when I need it.
I charge the battery pack separately with the charger I already have (if is compatible) or buy another one.
The one that came with the scooter looks like one of these generic an cheap chargers you find everywhere on eBay and Aliexpress, 58.8V 2Ah.
Could you kindly link to one of these battery packs on eBay or Aliexpress, don't look at the price just to the right one which is compatible with the scooter's motor then I do my research.
So the only important thing to look at is the voltage right? As I said the original battery is 52V 30Ah (from the scooter description) then I choose the Amperage depending on how much I want to spend?

On aliexpress they suggest that it is to be used with a 5A charger.

Originally Posted by Bohdan

On aliexpress they suggest that it is to be used with a 5A charger.

Thanks for the link.
From what I understand I can't pick a smaller Amperage battery because they pack it with a BMS 30A which won't be suitable.
The package you linked seems adequate, they pack it with a BMS 40-50A.

The motor on my scooter is 600W nominal and 1,600W peak.
The merchant on Aliexpress gives the choice of 52V 1500W 40A BMS and 52V 2000W 50A BMS, the price is the same.
So which can I choose? If I pick the more powerful one, is any problem?

1600w motor will draw ~30A at 52v so the batterie's higher capacity BMS will never be used.

Originally Posted by Bohdan

1600w motor will draw ~30A at 52v so the batterie's higher capacity BMS will never be used.

Excuse me if I ask a stupid question, if I choose the 30A BMS (and I can order smaller batteries) it isn't safe so better bigger like the 40A BMS?
I think that the merchant you linked to might be willing to assemble batteries packs will little changes like the smaller battery pack but with the 40A BMS.

Originally Posted by malb

14 cells in parallel giving around 48AH or 14 cells in series giving 52V, so would require and array of 14 p x 14 s to achieve 52V at 48AH, i.e 196 cells..

Could you guys please explain this to me, to a noob?
14 cells in series and 14 cells in parallel: 14s14p right?
What I don't understand is why they became 14x14 = 196 and not 14+14 = 28 cells?

14 cells in series are then connected in parallel 14 times i.e. 14x14.