ok so doing a little math here:

Looking at the Diesel Giant page:
http://dieselgiant.com/glowplugrepair.htm

We see that glow plugs should read something under 1 Ohm. Let's say they should be .5 Ohm.

We got 5 of these plugs in parallel. The math for parallel resistors brings us down to .1 Ohm now. V = IR so we got 120A draw from the 5 plugs.

120A for 3 minutes? Really?

Ok so I got a 65A alternator. Let's be generous and say it is generating 60A most of the time (which is totally unlikely. 60A when idling?)

So it would take a minimum of 6 minutes of running the car to charge the battery back up from the drain on the plugs.

And that's assuming 1) 100% efficiency of charge/discharge 2) ignores starter motor drain 3) no other electrical appliances used

Given all the generous assumptions, it seems like it would take a minimum of 10 minutes to charge the battery back up every time you start it.

Strange.