Loading NES Metroid with full energy tanks

Solution 1:

The password format has been thoroughly documented, and there are no bits used to specify Samus' actual health.

In other words, you have to farm health every time, or start using emulator features like save states or memory modification.

Solution 2:

Since I'm about to go fight Kraid, cue fifteen minutes of farming enemies for HP.

There's an E-tank in the room you fight Kraid in so just get it when you enter the room. IIRC getting an E-tank refills your HP to 100% - even if you are at the max 6 tanks.

For a similar reason, save the one in Brinstar for right before you go fight Metroid.