^ Many users will do fine by with a battery with less capacity. If you don't need extremely long run times, form factor may be more important with regards to how well everything fits in the recording bag.
Things may have changed a bit since I ordered my Talentcells, but at the time there were basically two or three basic case sizes and they offered several different battery capacities in each. The one linked above was (is?) the highest capacity in that particular form factor at that time (one could order the same size case with less capacity at a bit less cost). It's about as thick as the F8 is tall.
The next case size down is popular with many TS members running smaller recorders, and is likely to run a F8 for I'd guess 6-8hrs (this is a total guess). It's looks to be the same length and width but is half the height - similar in size to a small external USB powered HHD.
Ted has long been a good go to for power cables as well as audio cables. Unfortunately, the link David posted above is dead. I looked briefly but was unable not find the thread Ted was maintaining which indicates power connection requirements for most of the equipment used by tapers (not sure if its the same thread linked above or not). Hopefully is not lost as it has been a great resource to TS.
I was able to reuse the same power cord between the Talentcell and F8 that I had been using with one of my DR-680s. I just can't remember if it was the DR-680mk1 or mk2 which use different sized connectors (owned both models). This powers it via the coaxial wall adapter port rather than the hirose connector. That connection does not lock, but I keep 8 lithium AA's in the recorder as backup, which never get drained as long as the external battery is supplying power or the AC adapter is used. Lithiums keep it light weight, retain charge for years if not used, and don't seem to leak nastiness like dead alkalines can.