Dodge Grand Caravan :: 1990 3.3L - Starter Draining Battery?

1990 Dodge Grand Caravan, 3.3L

Three weeks ago, I had the starter rebuilt locally by a shop I've used confidently for years, most of their business is rebuilds like this. Besides a substantial coating of oil on the starter which was no benefit to the contacts, the tech also found a broken insulator which presumably was the primary issue. I installed the starter and have had no problems since (three weeks).

Yesterday morning, the battery was dead - no click, no lights, no horn. I could be wrong, but I don't think the interior lights were left on overnight.

I put my 1 amp trickle charger on it for several hours and when I reconnected the battery, the horn sounded right, interior lights looked good....until I tried the starter. In an instant, I got the chattering clicky sound of a starter with inadequate power , then nothing, and the lights and horn were gone too.

After charging overnight -almost 24 hours now, that same scenario has repeated: first good horn and lights, then clicks from the starter, then very weak lights and horn.

Is this simply that the battery is down and needs more charge? Or could there be something wrong in the starter causing this rapid discharge? A few months ago the same electrical shop load tested the battery and it was surprisingly good considering its age. I don't want to put a new battery in the car if the starter is somehow damaging the battery. I do have another battery I can swap in, but for the same reason I'm reluctant to install that without some better idea of what's happening.

Does this point conclusively to the starter? Or is this clearly the battery? Is there some way to diagnose the starter without removing it? I'm sure the shop would fix any mistake, but I don't want to pull the starter again for no reason. The cable connector on the starter looks normal.