Sometimes when you use one it gives full shields and sometimes it just doubles your max but doesn't fill up. I'm not sure which it is supposed to do but now that you have to use them far more often it would be nice to change this to always adds shields equal to the amount it is adding to the max.

I never paid attention.
Although you make a good point.
If it's only 4 hours it would be nice if it doubled and filled up the shields.

For the record I tried and it only doubled but did not fill it up.

I've seen both things happen also.

I've noticed this too, and i'd like to know why it happens. I don't mind either effect being the "correct" one, (Obviously I prefer a full shield effect though hehe) but I do want more consistency.

This is currently a result of how the shield charge is calculated. You may also notice that your shields will recharge immediately after repairing, as well. This is because the shields are considered to be still "charging" at all times. So, when the max is raised, it fills in the difference when the shields were already full. Strange, yes.

I think what makes the most sense, is that it doubles both max and current shields; so, if you are full, you are still full. If you are at 50%, you are still at 50%. It will take the same amount of time to fill up given how shields charge relative to max shield.

At the moment, its usefulness has dropped considerably.
I mean, already shields are much less space efficient that hull, primarily useful Defensivly, wheras hulls are more usefull offensivly (repair as you attack, every 5 mins) It makes sense that the shield buff lasts longer, as in the absense of supporting artifacts.

I can understand that people might feel it needs a downgrade in duration, but 4 hours is too extreme. Its now a combat buff, that functions poorly compared to hull.

Please make it last at least 8 hours, so at the minimum it can help defend while you sleep.

Obviously you either have extra mining output for your ship or weak hull for your level to say that you just go ahead an repair as you attack.

At the moment I'm trying to save up to place "Star Lifter's" on my mining planets: they are expensive. (look them up in the wiki)
Also when I have to repair my 4 HyperChannel Relay's it's 3.6B each time. I take my relays offline every time I rank up a level.
I would love to see the shields go back to 24hr personally. This longer time frame is especially needed by lower ranked players. But on the other hand higher ranked players can recharge 480 energy points (like I do) in 4 hours. Also with lots of shield tech and the shields completely recharging in less than an hour it's a whole lot of fighting/attacking I can do. But now I feel tied down to come back every hour or so to take advantage of the shield amplifier. Terrible feeling for a game. Many times since the change I said forget it and didn't use it because I had things to do and was only checking in; I wasn't going to be around for the next four hours. Dan if you keep the shield amplifier at 4hr then quadrupedal it to 4x the players current shields. I quite other games on facebook because of the tied down feeling.

I think either 8 or 12 hours would be better than 4, not really worth much for only 4 hours.

IMHO