Does depend on the genre, but I guess the main exception is TBS, where I expect a full mana pool at the start of each battle and likely no regeneration during it for regular units, except by some special ability or event, though the hero(es)/leader(s) may, possibly, also get some kind of regen, likely depending on actions and/or abilities, not something set per round.

In a real time RPG I strongly prefer regenerating mana along with a reasonably sized pool, so full mages will be able to crack out several powerful spells out of the pool if they're at max while the regen will compensate for the cost of low level spells that they'll be able to use on a steady basis, then when the battle's over wait (or explore if you think it sufficiently safe) a while to get back to full and tackle the next one. Hybrid classes would then be able to cast a couple of more powerful spells out of the pool and have the regen compensate for some low-level spells mixed with non-magic abilities.

On the other hand, using stamina for everything, be it magic or non-magic abilities or plain running, also has its appeal, in which case it may mean no regen while you're actually doing anything but regen kicking in if you can stop for a moment (and also not be attacked), even mid-battle, and the regen may be much faster than the mana regen I mention above, so you can catch your breath for a few moments and be able to do a fair amount again.

In the JRPG-style games you favor though, not sure... No way seems really right. I'd definitely expect continued tracking of mana, not it being reset at the start of a battle or entrance of an area, and would also want some regen instead of only restored by resting or item use, but how that regen would go, couldn't say. The turns make every option I'm thinking of seem wrong/fake...