E bike battery current limiting

[SharkBike]

Hello.
I have a cargo bike using the Bosch Classic system and I thought I would attach a generic Chinese pack in parallel with my pack to boost the range without having to change over the Bosch battery and also to supply power to 3 switch mode power supplies that step down to 12V for some LED lighting that I have attached.
The problem is my generic pack appears to behave as if a resettable fuse has been triggered when I attach or switch it into the circuit. The output drops right down then seems to rise up to 6V and stay there.
I am assuming that there is an inrush current problem. I should add I have to two packs protected from each other by some ideal diodes. Any suggestions how I can get round this? The Bosch pack has no problems

 

[chris_n]

I would suggest you look here https://www.pedelecforum.de/forum/index.php?forums/bosch.30/ using google translate, someone here will have tried what you are doing.

 

[Deleted member 4366]

The two batteries need to be at the same voltage when you connect them. You can't switch one in and out. Also, you must disconnect them when charging either.

 

[chris_n]

The two batteries need to be at the same voltage when you connect them. You can't switch one in and out. Also, you must disconnect them when charging either.

I'm not sure if this works with a Bosch as I don't have one. Hence the link to the German forum.
d8veh is totally correct the batteries must be at the same voltage when you connect them and they must be charged separately so that the BMS for each system can do it's work and keep the batteries in balance.