Re discharge depth, lead acid (eg. AGM or Gel) are basically flat at 50%. Lithium (ie. LiFePO4) can go down to around 20 & 30%
When you include depth of discharge and the number of rated cycles for a battery, lithium iron phosphate work out cheaper over their lifetime
(DOD - charge cycle as - look them up in each battery spec)
And a warning, don’t buy cheap batteries from a Facebook add. They are likely to be fake.
Some batteries like enerdrive & invicta have built in power meters accessible via a Bluetooth app.
Also note that some batteries will allow parallel and no series connection (and series with no parallel)
There are some good sources of information from companies like victron and bmpro on the internet
Cheers
Greg
Edit: some Links-
Victron AGM verses Lithium
BMPro information
Victron info on wiring