Health does not regen and when they buff your health they increse you max health.
Please don't share wrong "facts", thank you.
You have health pips that will regenerate over time, though it is not all of you health pips that do. im not sure what percentage of your health pips are regeneration ones though. The only way to get back to full health after you have lost some non regenerating health pips is to be healed by a medic.
You have one main health-bar, which does regenerate.
Additionally, you have health-"pips", which are filled by medics when buffing you.
What we don't know (yet) is, if those "buff-pips" do regenrate if they're not completely gone.