Crazy Idea to add Rack battery to Delta Pro

[DBarr]

First off, Thanks to everyone here. This is a wonderful site for information and I am learning alot.
They say there are no stupid questions but maybe I have one.
I just watched a video of the teardown and had this crazy idea.
Can I attach a 48V rack battery directly to the battery terminals in parallel inside the delta pro?
We connect rack batteries in parallel all the time as well as other types. So why not?
Looking for thoughts and reasons not to. If I open the case and connect directly to the battery will it charge both?
I know it would lose the ability to be moved around, but I don't know if it will hurt anything else.
Thanks for any input. I would love to see Will try this in one of his videos.

 

[400bird]

You would need to use the same quantity in series and the same cell chemistry.
The standard Lifepo4 at 16s would be very, very low at 46 volts (2.8 volts/cell)

 

[DBarr]

The person checking this unit with a meter has purposely run the battery down to disassemble for the video.
DELTA PRO has a battery capacity of 3,600Wh (48V 75Ah), Battery type: PCF 15 cell, and I believe it has a System Voltage: 48V · Nominal Voltage: 48V · Chemistry: LiFePO4 · Charging Voltage Range: 54.8v @ 3.65v per cell.
Cell Chemistry for both are the same, only difference is 15 cell 75Ah and 16 cell 100Ah.
I guess what I am asking is: Will a 16 cell BMS and a 15 cell BMS play well together if connected in parallel? ?

Will both charge and balance, protected by the BMS of each?

 

[400bird]

Cell Chemistry for both are the same, only difference is 15 cell 75Ah and 16 cell 100Ah.
I guess what I am asking is: Will a 16 cell BMS and a 15 cell BMS play well together if connected in series parallel?

Fixed that for you.

But to answer the question:
Not well.

The 15s pack will be working alone in the lower SOC as the 16s external battery's BMS will disconnect at low SOC due to low voltage.

The 16s cells will likely spend a lot of time at the bottom of their cell range and never reach the top.

Will both charge and balance, protected by the BMS of each?

With mediocre results, it would probably work.