the battery meter represents energy, Energy is needed to use most of your augmentations as well as take down opponents...
There are consumables that you can pick up to recharge your energy...
Cyberboost ProEnergy Bar fills up one energy bar
Cyberboost ProEnergy Bar Pack fills up two energy bars
Cybertech ProEnergy Jar fills up 3 energy bars
Also if an energy bar is not completely used up and there is even a little left, it should automatically recharge over time... but if it's used up all the way it will not.
Just as oogadebob said, those consumables help but eventhough you have all 5 batteries, you will always have one at full capacity.....drink all beers, take all pills and use the Cyber-s when you need too, by the time you're done you will still have a good amount off Cyber-s (well I did)