how does the health bar in AC2 increases ?
in the place where Enzio first meets Rosa.
Collect Codex Pages (4-5) would increase 1 health bar or buy Armor.
decrypted 4 codex page but no increase in health bar
Health gauge increases when you upgrade your armour from the Blacksmith. Gather enough Florins and visit a Blacksmith (check your map legend to spot one), select Armour upgrade and check the stats on the right hand side to know how much health bars it would add. If you have enough dough, then purchase it and it would automatically be equipped.
collect all the assassination tombs, go to Villa De Auditore and unlock Altair's armor!!
Superb armor.
Will surely increase your health!!