Additionally there are shield cell banks that you can equip and use to rapidly charge the shields. I tried it 1-2 times but couldn't understand when exactly are they supposed to work -before or after "shields are offline and charging" alarm..
Shield Cell Banks work like an instant boost to a damaged shield, but have no effect on a shield that is already off line.
Your HUD shows 3 shield rings to indicate the state of your shields. If you are in heavy fight and your shield are taking serious hits from multiple targets, you should use the Shield Cell Bank as soon as you lose the 2nd ring.
If you are playing the game with a friend, you can both jump into a Private Group, or create one yourself, and meet up. You can then face each other at 3km apart and have your friend shoot at you until your shields begin to fail.
You can fire off the first test after the first ring on your shield are lost and see how long it takes for the cell bank to bring your shields back up to full.
Repeat the test, but wait until your shields lose the 2nd ring, then fire off the cell bank and again see how long it takes for the shields to repair and come back up to full.
Obviously, you want to do this with someone you trust so that they do not just destroy your ship in the process, which is why I recommend doing this with a friend.
In the past, this is how some of the high end players have tested changes and/or issues and you can sometimes find threads reporting findings from those players using the same type of testing that I outlined above.