After a bit more research I have found some of the theory behind shield recharging.
The value of 0.9 MJ/s on a 3E Power Distributor on a Cobra is the rate at which systems recharge shields. The default shield generator is a 4E with 93.58 MJ total strength. In theory therefore, a 4E shield should take 104 seconds (93.58 / 0.9) to recharge.
A class 3A Power Distributor pumps out 1.3 MJ/s, so the same shield with an A rated distributor should take 72 seconds.
Until I’ve tested this theory, I cannot be certain, but it follows that the increase in shield from the boosters would make the recharge time increase based on your power distributor’s ability to fill it back up.
Shield recharge times
Boosted shield recharge times
As you can see, if this is correct, the Cobra with 4A Shields and a 3A Power Distributor should recharge in 97 seconds. With a 0A Shield Booster, the shields are raised to 150.6MJ so will then take 116 seconds to recharge on the same ship (19% longer).
My Fer-De-Lance with 5A Shield Generator, 6A Power Distributor and four 0B Shield Boosters will therefore take four minutes and three seconds to restore shields!
My next quiz question is are shield cells based on a percentage or a fixed number of MJ? If the latter is true, then the more Boosters you use, the less effective even the best Shield Cells will become.