oshyshko, you really do need to use an interface like I linked to, something that will be able to connect and measure the six LiPo cell which are connected in series. There are other chips and other little ready made products that essentially do this and you could connect to them with an appropriate interface, such as serial or I2C or SPI, usually via an electrically isolated interface.
I do not see that it will be possible to connect the Arduino directly to the Lipo cells to be able to measure them individually.
Remember the analogue input on the Arduino is a simple single ended input and has no input front end, in terms of protection or buffering or scaling.
If you read the data sheet for the LTC6802 and family chips you will gain some insight into how they do it and why you also will not be able to do it by using the analogue input of the Arduino.
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Paul - VK7KPA