I just replaced the batteries and tested it alongside one of my other detectors. It seems to be in full working order, no longer giving false beeps. Thanks for the suggestions!
Ace
Some fool on YouTube was using an F2 and was out in knee deep water when he dropped it.
It was only in the water a second but that was enough to kill it.
A few days later he tried it and it started up fine, seemed to beep over targets ok so he thought everything was good.
Then he decided to test it against an Ace 250, film it and post it on YouTube.
Watching the vid it was obvious to anyone that ever used an F2 that the F2 was not working right...at all.
Way too much falsing, couldn't pick up any coins past two inches or so, super jumpy ID on the targets it could pick up.
The Ace came off looking great but the F2 came off looking like absolute junk.
I left a comment and asked if this was the one that took a swim just a few weeks before and he admitted it was, then I told him to send it in because there was something really wrong with this thing.
Also I told him that this whole video was deceptive since he never mentioned anywhere in that video that this was the the same F2 that took a bath just a few weeks before and anyone watching it will assume that the F2 actually worked that badly.
He still left that vid up for years.
Just because just turns on doesn't mean yours is working as well as it did before.
You would have to test it thoroughly against a known perfect working unit to see if it actually is working correctly and up to specs.
If a friend of mine borrowed a detector from me and drowned it I would expect nothing less than that friend paying to send it back to the factory and to at least have it checked out thoroughly and also pay to have it repaired if it needed to be.
Mistakes happen but adults take responsibility when they do.
You should tell the owner what happened when you do return it, be honest and see what they expect out of you.
I am sure this has happened before to others, those that return borrowed tools that had caused some major issues but never let on to the owner that anything happened hoping to get away scott free are not adults and are not friends.