1.Replacing Glow plugs will not "Kill" batteries.
(could you have disconnected something in your endeavors?)
Empirical approach would be:
1. check electrolyte level in battery
2. charge battery overnight (with a fully automatic charger)
3. load test battery in A.M. ('might take it to AutoZone, Etc. for free test)
4. check electrical connections in Battery/Alternator/Stater/Engine systems
for "clean" / "dry" / "tight"...don't forget the grounding (Negative) strap
from the engine to the chassis.
5. locate and check the glow system fuse on the lefthand wheelhouse under
the hood.(it can have an invisible hairline crack that prevents "glow".
See if the charged battery will activate the starter to turn the engine over.

If a properly charged battery ,with good connections will not activate the
starter,I would look at it with an evil eye...try whacking the Starter body,
not the Bendix,with a light hammer,while cranking.If you get action then,
it may be the starter.

All of this assumes no problem with the mechanical or electrical portions of
the ignition switch.