Xiaomi mijia m365 external parallel battery pack

[nkgeorge]

Hello, first of all i'am a noob so be gentle
I've bought a xiaomi electric scooter , and for my weight i can run it for about 18km on full speed, i've read for the past 2 days online how i can make a external battery pack, but i still have some questions :
1. both packs needs to be the same ah? , the original is 7.8ah if i want to make a 10s4p 11.6ah , will both packs deplete at the same time or the 7.8ah will deplete faster and therefore i can't use the extra 3ah from the second pack for extra range?
2. will 2900mha 10a be enough for 10s3p or 10s4p , or i need bigger amps batteries ? motor is 250w with peak 500w
3. i've heard nkon site is trusted , but do you recommend buying refurbished batteries from them?
4. what bms do you recommend for my pack? how many amps

any other info will be great

 

[fechter]

The batteries don't need to be the same Ahr, but need to be the same voltage. If you put the two batteries in parallel, they will always have the same voltage and they will discharge at the same time. The voltage of the two packs must be pretty close before making the connection.

If using parallel packs, each pack will only have to carry part of the load. I'd recommend using the largest capacity that's practical, but 2900mAh should be OK if used with the other pack.

You could also have two separate packs that are not parallel and used sequentially. This is not as good but can work if both packs have enough power to run the motor.

I have no experience with Nkon

For parallel packs, I would use a single port BMS with at least 20A rating. These are inexpensive. With a single port, you can leave the packs always connected and charge both at the same time with the stock charger.

 

[nkgeorge]

What i saw (how it's made) until now , the second pack has it's own bms ... then a Y cable with xt30 connectors goes from both batteries/bms to the scooter mobo. Something like this https://medium.com/@andriiliakh/installing-additional-battery-on-xiaomi-mijia-m365-a8782f3b75b0

i've read today on the forum that if second pack has more aH when the first pack with less aH is depleted the second pack would not work anymore (witch made no sense to me... but i'm a newbie and tought that i better ask )

thanks, and sorry for my bad english

 

[fechter]

That makes no sense to me either. Y connection should work fine.