will battery casings increase the lifespan (not standby/active use) of phone's built-in battery?

As batteries are built into mobile phones nowadays & to replace them
requires it to be brought to the workshop who has the tools to change
them,  I'm thinking of getting battery casings so as to reduce the
number of charge+discharge (that is what typically reduce the lifespan
of batteries.

Specifically I'm looking at Galaxy note 9 ie batteries like those below:
https://www.amazon.com/dp/B07GB5R27M/ref=psdc_7073958011_t1_B07H3256JB
https://www.amazon.com/gp/product/B07H3256JB/ref=ox_sc_act_title_1?smid=A2QAZ8RQ4KWQ44&psc=1
https://www.amazon.com/dp/B071NWVT9M/ref=psdc_7073958011_t2_B07H3256JB 

Q1:
Am I right or mistaken?  With above battery cases, will the phone  charge
directly from the casings' batteries rather than charging from the built-in
batteries?

Q2:
Or it'll shorten the built-in battery's lifespan instead as the casings will
charge the built-in battery whenever the built-in battery goes down by
1-2%, thus maximizing the number of charge+discharge cycles?

Q3:
Any other ways to increase life span of built-in batteries?  Understand
we should let it discharge till almost 1-2% before charging it up again
& we should always charge it to the max of 100%: this is a known
good practice but often this is rather inconvenient & risk discharging
completely, resulting in phone being powered off, missing crucial
calls/messages.

What I do know is if laptops are frequently being left connected to
AC or even an external powerbank (Hyperjuice, Vinsic Warrior with
AC output ports) sources, it certainly reduces the number of charge
+discharge cycles (as measured by BatteryInfoView software) &
increases the laptop's life span.