Ok the health topic 
Basics first:
Lights have 120HP, mediums 140 and Heavies 180.
You can have up to 5 bonus pips. The first gives 35HP, then 30, 25, 20 and the last 15, altogether 125 worth. So a light can have a maximum of 245, a medium 265 and a heavy 285.
So to your question:
You can get one pip by the “battle hardnend ability”.
Medics can buff you another one, with “improved life buff” even two.
The health command post gives one more and if an engineer with the upgrade ability upgrades it, it gives you anotherone.
So you always can get one by your abilities and on most map stages one from capturing a health commandpost. For the other 3 you need medics and engineers in your team 
You see, an upgraded health command post can really turn the tide when a team gets dominated.
(Guess thats why the bots were so eager about them. They knew more about the game then most of us:tongue:)
Keep em dropping!
PS: The supply command posts are vital too as they enable your team to buff more and use more grenades…