36 volt 6 ah battery and a 36 volt 4.3 ah battery in parallel on a 350 watt brushless motor.

[sore knee bike ride]

Will a 36 volt 6 ah battery and a 36 volt 4.3 ah battery in parallel on a 350 watt brushless motor will function properly?

I am fairly certain that both batteries have a BMS and protection circuit

They have xt60-u connectors

These are the two batteries I want to combine in parallel.

The batteries likely have different c ratings

When one battery drains faster than the other the battery with less power, one might try to charge the other.

If the batteries have a difference in voltage wouldn't they balance each other out? I think batteries are not affected by being charged with minute currents.

And I guess would the controller demand different current percentages from each battery?

Would the different c ratings pro rate the amount current supplied by each battery?

And most importantly would there be any damages or Ill effects to the batteries ie. Slower charge times, loss of capacity, change in characteristics?

What if I put a diode on each battery to stop the charging effect from another battery?

 

[Gionnirocket]

Me, I would avoid that set up in parallel. Period.
For safety and reliability you are much better off using one, then the other.

 

[Gionnirocket]

I Google this it might be helpful. It was read out loud on my device by a very pleasant lady with British accent.

There's much less of an issue using quality hardware all around... this shouldn't be a budget venture with no name, low grade mismatched cells.

 

[sore knee bike ride]

So with the diode I read that one direction has a large resistance and the other direction has a low resistance. I could not find info in regards to what will happen to efficenciency.

Combining diodes in parallel will result in in both the forward and backward resistance declining.



My thinking is that if the backwards resistance becomes to low the circuitry could have an Ill effect.

I theorized that even in factory packs not all cells are created equally. So my thoughts are that when the cells are connected in parallel within thepack, the batteries with the higher capacities will provide more current.

And if that were to be true, between the white and blue pack, current draw from each cell would be proportionate to the capacity of each cell.

Also the pack are meant to shut off when the cells get to low.

What could be the downside of one pack charging the other? Damage to circuitry?

I mean the difference to me of buying a new pack is quite negligible.

 

[harryS]

You can buy those diode rigs ready made. Seems like the market price is around 38 bucks.

Ebike Dual Battery Connection Adapter Parallel Module Increase Battery Capacity | eBay

Wire 2 Batteries in Parallel / Double Capacity. When One Battery Runs Out During Riding, It Will Automatically Switch From One Battery To The Other To Power Your e-Bike Again. 1 x Dual Battery Connection Adapter (as your choose).

www.ebay.com

 

[sore knee bike ride]

But the diode parralel adapter will maintain voltage longer. The bike will keep top speed longer.

 

[sore knee bike ride]

So I guess the more simplified question is:

Will connecting :

"Battery A": a 36v 6 ah pack
And
"Battery B" a 36 v 4 ah pack

in parallel cause damage to either battery A,B or the Controller of an e-bike?

 

[harryS]

The answer is maybe. That's why external protection circuits are needed.

.

 

[sore knee bike ride]

I wonder how this battery:

https://www.amazon.ca/Lithium-Ion-Battery-150W-500W-Rechargeable-Replacement/dp/B0B73DD6PV/ref=mp_s_a_1_4?crid=38V4QS2S2LPCN&keywords=36+volt+battery+30+ah&qid=1676823362&sprefix=36+volt+battery+30+ah%2Caps%2C159&sr=8-4

Compares to this battery:

Lithium battery - 36V 10Ah, 13Ah, 18Ah

Lithium battery - 36V 10Ah Samsung cells Lithium battery - 36V 13Ah Samsung cells Lithium battery - 36V 18Ah Samsung cells Please contact us to get the accurate size

richmondebike.com

Both are the same in capacity but the price is 7 fold.

 

[harryS]

The blue battery is obviously a lie just from the 30AH rating and price, If you bought the best cells in the world, the bset you could fit in that package is 36V14AH, but those cells retail for $5-7 each, and there are 40 cells in that battery. You're getting 50 cent cells if they can sell it for $100CA. Just look at the review. Buyer says it's 7.5AH, and that's new. A year from now it will be either dead or 5AH,
.
The 36V10AH battery in the second link also has 40 cells. They are Samsung. Probably cost $3 wholesale. So $120 for cells, and $80 for the case/labor. Factory makes its it for $200. Sells it to the vendor for $260. He charges you $429. To get 18AH, they increase the cell count to 50 cells and use more expensive cells..
.
You can buy that 2nd battery on amazon/ebay with for around $200-250 for 10-14Ah, but not with Samsung cells. You get $1 cells. Might last 3 years. I bought one in 2021. You wouldn't buy that battery unless it fits your ebike as it uses a dedicated mount.