Efficient charge/discharge Li-Ion battery

[AGRAIL]

Hi ,
I`m dealing with one schem of efficiently charge / discharge of lithium assembly (6P) and stuck with one problem.
In case charge / discharge Li-ion there are already many different devices , but main problem with them is heat - all discharge will go into heat.
This is not problem with one battery - but can cause an real problem in case scaling this job .
So idea is to use hybrid inverter - solar input as load and AC output and source for charging .
In case of high input voltage of inverter can be manage with serial connection of few assemblies and higher q-ty input BMS .
But main concern how to limit solar input current -  many of them use mppt and draw maximum power of the solar input .
This can shutdown BMS and stop discharge.
Maybe someone use more hybrid inverters and maybe some vendors have some SW limitation for solar input ?
Thanks in advance .

[Siwastaja]

This just word salad, completely non-understandable. Please try again, what is the battery and what it is used for?

[radiolistener]

So idea is to use hybrid inverter - solar input as load and AC output and source for charging .

This is a bad idea, because AC inverter has very poor efficiency, especially if you're converting AC=220V from 6S DC=6×3.7V=22.2V.

Much more efficient way is to use DC/DC from 22.2V to 5V, 12V or whatever you want. This is because conversion efficiency depends on voltage ratio. 22.2 / 5 = 4.4 which is better than 311 / 22.2 = 14 (220Vrms = 311Vpk). In addition, there will be additional losses because it also requires 50 Hz sine wave AC instead of DC.

For 6P it will be even worse, because voltage ratio will be 311 / 3.7 = 84, too much power will be lost due wire heating and bad conversion efficiency.

[AGRAIL]

Purpose - I need to charge / discharge 6S3P battery few times in a row and verify capacity of them . In case of one battery - it`s not a problem to use china battery testers 150W . But if this job must be scaled - all this energy lost as heat can be a problem.
So idea was somehow ( at least some part of energy ) transfer between batteries.
2nd idea was to connect 4 batteries in parallel with own BMS to AC inverter -> inverter connect to battery charger , which is connected to 4 parallel batteries with own BMS .
I was thinking about some DC-DC converter - but for such currents I can`t find widely available models . In my case it`s much easier to buy AC inverter and battery charger . When discharge cycle will finish - I`ll switch charger into grid for charging finish . After finish - I`ll reconnect batteries between the sides.