Ali express - buying a new battery in the future.

[graywok]

There are a number of posts on here where the knowledgeable point the person to Aliexpress items.
When searching there appear to be multiple sellers on Aliexpress selling an appropriate specific battery for my bike.
How do I tell which is a decent seller?
Many thanks
Cheers

Graham

 

[Woosh]

Avoid buying batteries from China, no matter how good the price is.

 

[Bonzo Banana]

The issues with Aliexpress battery packs is they are mis-sold and underspec, manufacturing maybe poor quality and the cells may not be as stated. However on the opposite side I have seen reports of people who have bought them and have been very pleased with the battery packs and have lasted a long time without issue. It's a gamble basically.

One thing that bugs me is how many sellers describe their battery packs i.e. they will state the Ah without factoring in the final voltage of the battery pack. So for example a battery pack containing 20x2500mAh cells will be sold as a 36V 50Ah battery pack or 36V 50000mAh battery pack when in reality it is a 36V 5Ah or 36V 5000mAh battery pack because there are only 2 cells in parallel with 10 cells in series. Also those so called 2500mAh cells could actually be 2200mAh or worse.

The issue becomes greater when you have a mid-drive motor or unrestricted direct drive hub motor which can pull very high currents at times which these cheap battery packs cannot cope with they just don't have that discharge capacity so it overworks the cells and can lead to early cell failure and generate additional heat.

The issue is made more complicated in the EU due to the 250W rating which is applied to motors from as little as 140W to motors as high as 900W. You need to ignore the 250W rating and look at the controller spec. If you have a 250W mid-drive motor with a 20A controller that is 720W (20Ax36V) or 960W for 48V systems (20x48) and then you have to allow for momentary peak current above that, maybe an extra 40% wattage or current. You maybe looking for a battery pack with a sustained discharge rate of 30A or more for safety maybe approaching 40A discharge rate for safe over-capacity.

You basically need a very high spec battery to supply the required current for such motors. Many aliexpress battery packs over-state their discharge capacity or state the discharge capacity of cells which they aren't supplying, they are using a cheaper Chinese brand cell of slightly inferior spec. There is a very reliable 2500mAh Samsung cell that many packs are advertised with but in reality there is a Chinese brand cell that is similar but slightly inferior in spec that you are more likely to get.

Key advice to buying on Aliexpress is to look for a seller that has been selling for a long time, a few years who also has high rating reviews for its battery packs. Don't buy from a seller that only appeared last month. Also do the maths for battery packs. I think the maximum 16850 cell capacity is something like 3600mAh so if you buy a 36V 20 cell battery pack (10s2p)the absolute maximum capacity of the pack is 7.2Ah (2x3600mAh). Anything above 7.2Ah is going to be fake because it can't exist. Look at the cell type and how many cells are in parallel and then look for the maximum capacity of that cell be it 16850 or 21700 and you soon find out a huge number of sellers are making false claims well beyond the capacity of any such cell.

 

[saneagle]

There are a number of posts on here where the knowledgeable point the person to Aliexpress items.
When searching there appear to be multiple sellers on Aliexpress selling an appropriate specific battery for my bike.
How do I tell which is a decent seller?
Many thanks
Cheers

Graham

Probably better to just tell us what you need and get advice on where to get it from. Aliexpress works well when there is something specific that you need and it's not available from other sources. By the time you've paid duty and handling charges, batteries are often cheaper and quicker from UK suppliers.

 

[sjpt]

batteries are often cheaper and quicker from UK suppliers.

and much easier to handle any issues if you do have them.

For example: I recently bought a replacement battery from Woosh. They accidently sent the wrong one; a pity but mistakes do happen. I contacted them. The next day the courier delivered the right one and collected the wrong one.

 

[guerney]

You're only allowed a short period of time to leave a review on AliExpress or Ebay after your purchase, so if previous customers experienced issues, it's less likely you'll ever know... and that's why I bought my cheap battery on Amazon marketplace, which allows reviews long after purchase, also allows edits of those reviews long after that - I'm still adding to a review for something I bought over three years ago. Plus the price quoted for stuff from China sold on Amazon marketplace, has always been the price paid. Unsure how refunds for items bought on Amazon Marketplace go, all my purchases have been ok, so I've never had any need to demand one. Can't recall anyone on these forums reporting horrible problems with a cheap AliExpress battery, apart from billyboya, and he was using his on a Emoped drawing high amperage. Everyone else drawing 7 to 15A seem to have been fine, but I've only been stalking this forum for about three years.

That said, I'll attempt to buy my next battery from someone who claims to be in the UK.

 

[graywok]

Thanks all, summing up, it does sound best I contact the original bike supplier in that case which is actually Woosh.
I am not yet in the process of buying a new battery as mine is still going strong after 4 years however I wanted to do some research now in advance.

Thanks again all.

 

[graywok]

Probably better to just tell us what you need and get advice on where to get it from. Aliexpress works well when there is something specific that you need and it's not available from other sources. By the time you've paid duty and handling charges, batteries are often cheaper and quicker from UK suppliers.

It was for a Woosh RIO mtb 4 years old- it's a Reention dorado cased battery at 36v ( short variety 390mm) currently 17ah . I notice there are new varieties on sale utilising either A)the 21700 cells or B) a 'Max' case offering 21ah capacity and this sparked my interest.
Not buying yet but doing the homework in advance so I can source a replacement when I need.

Current preference is buying through Woosh as they have been great in support to date.