12 volt battery well rusted out- Houston, we've got a problem

Thought I'd share this. Went to replace the battery when car died- not too worried as it was long overdue. As I looked into battery well I see daylight (not good). I hoist out battery and peer down into battery well. The bottom of well completely GONE- as in rusted out. Battery must have been sitting on chassis below the well to keep it from dangling onto street. Not sure how to deal with this.....don't want to spend a fortune. Perhaps some metal straps supporting a rectangular metal plate for battery to sit on- not sure.
Pic #1 is of normal battery well
Pic #2 is what is left of the metal prius body- the bottom of the battery well- bolted on to the battery clamp assembly. Any suggestions welcome. 2004 Prius with 110,000 miles.

 

thanks- sounds like best bet. Though always a little paranoid drilling into metal when not 100% sure what is behind it. I think I'll fabricate a little hole in plate with nipple (to keep water from entering) for any water to drain. That 'flex seal' infomercial comes to mind! Maybe I'll paint the whole battery well with the stuff after riveting in the sheet metal w/bracket. I'm not sure if damage was cause from moisture from above or below....likely above. Thanks again. So much for quick battery change.

 

*

 

Appreciate these links, but the whole bottom of the battery well is simply gone! As in I'm looking at the road and chassis-simple battery tray won't do it. I'll use the standard prius battery clamp assembly bolted to fabricated sheet metal bottom I guess. Also, I don't have a smart key- hence my battery was smaller and the clamp assembly tray is also smaller. Prius batteries (non-Toyota) seem to all be the larger smart key version. (same height ,width, just a bit longer) ...so I'll get the larger tray from toyota. Stong deja-vu here......I had a 1988 Toyota cargo van.....engine would not die- great travel vehicle.....finally rust ate it up.[

 

Here is a clear picture of the carnage. Yes, that is the chassis and the road you are looking at where the bottom of the battery well should be....ugly. Think I found problem, rear wheel 'mudflap' (?) is missing. All the salty winter water spray has been blasting bottom of battery well. Current plan of attack: 1) wire wheel away loose rust 2) clean with alch & rag 3) apply ospho- I used to fish in Alaska, this stuff works great on rusting ships 4) paint 5) fabricate sheet metal pan with large 'tabs' up sides 6) bolt on prius battery clamp assembly to pan 7) paint pan 7) undercoat pan 8) rivel two cradling steel straps under pan to attach to sides 9) rivet pan tabs, steel straps in place 10) replace mud flap!!!
p.s. appreciate all the suggestions! In a way, I'm glad I discovered the problem when I did -2 blocks from sheet metal shop. 2 months back, I was driving in unpopulated Maine backcountry at midnight (returning from CAN). Battery falling out onto road might have been problematic.

 

Appreciate response, but in my case I do not think it is a leak. Raining pretty hard yesterday, and did not see anything. Does the Prius have a mud flap? Right behind my rear tire behind the lower outside of car is open! In other words, the salt spray/ gravel kicked up from tire would kick up and hit battery well bottom. If there is still a leak, I'm planning to install a little hole w/ plastic nipple to drain any water from new pan just in case. My tire well is fine (phew!)...... Been formulating solution in my mind. I have to keep in mind car bounces and battery is heavy- so I really have to secure things.
1) with wire wheel grind rust off
2) wipe clean with alch soaked rags and apply 'Ospho' (though it's hard to find)
3) paint with rustoleum
4) construct cardboard mock up of pan design.
5) Will attach battery clamp assembly to bottom pan. Also want 2 metal straps cradling clamp assembly sandwiched between assembly and sheet metal pan- running up over edge to be riveted to horizontal surface over the lip of well. Sheet metal will have large 'tabs' running up sides to rivet on (getting washer behind rivet may be problematic)
Have sheet metal fabricators duplicate cardboard mock up
6) paint every thing.....rubber undercoat underside.
7) attach- love this Prius- will not surrender to rust
8) open a limited release 'Black Chocolate Russian Imperial Stout' by Brooklyn Brewery. Drink slow, and only one- 10% ALC by volume.

 

- Not 100% sure of it rusting from outside, just noticed no mudflap. Correction, the outside of battery well acted as the mudflap. Also, saw no water trickling into battery well in steady rain. Also, last time vehicle was jacked up......lots of general surface rust. This summer I'll be under there with 3" crimped wire wheel attached to a Makita, Ospho, and Rustoleum flat black....

All that said, I'll take precautions re the leakage Gen 2's experience, and silicone referred to areas....

 

both rear flaps missing......maybe they were never there? Just got some from ebay at good price- $10 each....Toyota stock.

 

$10 each....Toyota stock......(ebay)

I think I need more though.....I need to fill where the 'cutouts' are.... these are welcome though.

 

Thanks- good info.

~CSP new to me- thanks!....I agree re benefits of grease....in good ole days, people used to spray underside of auto with dirty -used motor oil. No rust. Bought this car last summer- new to me- so preventative grease 'should -haves' beyond my control.. 2004 with 105,000 miles.

~ wire wheel underneath labor of love. Wire wheel will go quick, ospho will wipe on quick, black rustoleum will brush on relatively quick. Surface rust progresses....as Neil Young says- rust never sleeps. Peace of mind well worth it. I learned my lesson with an old 1988 Toyota van. Engine was a gem -typical Toyota...great Travel vehicle.....rust took her from me. So now, I've learned to stay in constant combat mode. See rust- treat rust.

~ battery in tire space is an idea....but I would invariably having to tweak unexpected aspects: longer cables, etc.... so time /effort saving may not pan out (?)

~ more horrifying pics?! actually, bottom of battery well is it for carnage. It either filled with water- or else played 'mud flap' and took brunt of salt/ grit/ water spray.

Actually this sort of thing not unusual with New England winters. good info- thanks!