water in 12v battery well

that's rain water, there should be a rubber plug under the battery.
get the battery tested free at an auto parts store.
check under the spare tire as well.
it usually comes in thru cracks in the rain gutters under the black plastic moldings. silicone will seal them.
if not, it can be the hatch gasket or hinge bolts.
make sure the neg battery connection is clean and tight to the body.
once the battery is cleared or replaced, check the voltage at the jump point under the hood, with the car off

 

Remove the drain plugs on each side well the battery and under the spare container over there where the battery would go on the other side but there's not a battery and the spare tire well take the drain plug out of that you can just leave the drain plugs in their respective places they won't go anywhere and then water will pass through the system rather than build up and you should be good

 

no,the battery is sealed. not really a coincidence, many 08's leak, and now you have a separate issue.

 

The Priuses in many ways remind me of the old American motors pacers the fish bowl car the Prius is as wonderful terrarium water gets in it and it just steams up all the windows and everything it's like you could grow plants or something in the Prius no problem and yes moisture will mess up the plug in above the battery that handles the battery fan that pulls air by the right side shoulder of the rear passenger blows it through the battery out the duct work and out the vent right above the battery that's in the way when you're changing the battery The plug right above that duct work is getting water in it You need to unplug it clean it well with electrical contact cleaner dielectric grease put it back together wrap it with zip tape and then move that plug as close as you can to the sheet metal of the body where it's out of the path of water drip and it'll just sit over there if you're worried about it you can tape it right to the inside of the body panel with the same zip tape that zip tape will not take on water. Yes all of that interior moisture is seeping in the plugs and connections so once you get that water passing through and not dwelling in the car the moisture content in the car won't be near as bad but I would start undoing plugs and spraying them putting dielectric grease or silicone on them and plugging them back up because funny electrical things will happen The battery's been sitting in water that's been freezing possibly frozen in water battery needs to be tested well and load tested if it fails replaced drain plugs out water should not build up back there and freeze in other battery

 

10.4 volts is low enough to wreak havoc on everything You need 12 5 plus sitting 20 30 40 minutes after the car has been shut off or better

 

Some folks don't like to remove the rubber/plastic plugs. Instead, they drill a hole in the center of them....1/4" 3/8", whatever. And call it good. Read one post where someone said removing the plugs would give mice a free "door" into the Prius.

Myself, I just removed the plugs, totally.

 

Uhh the 1/4 inch or less holes in quarter panel battery area yes right. Obviously keyboard jockeys. The only place large enuff is the spare hole .only.. I guess you could use 1/4 hole punch in rubber plug . Nice if you leaving car like that ok . Maybe on a farm . If ya cannot do better than I guess ya deserve the mice . I live in SE Usain the country wno garage .I've no rodents in any vehicles here. You shouldn't either or ya like ..

 

Kind of had trouble following that....

Drill holes,remove the plug. Whatever. I sealed the seams pretty darn good with GE Silcone II. Not pretty, but it works.

 

yes, fine to drive the car. reinstall the plug and install a new battery.
check the area once in awhile and if water is gathering, remove the plug, let it drain and replace it.
eventually tough, the battery might fall out

 

That looks like the stock Yusa battery that came with the car lol. If so it’s 13 years old so you win the longest stock battery in a g2.
How many times have you jumped it?

There is hundreds of posts about leaky G2 cabin. Check under the spare tire that’s all rusted too. If it gets too bad the water can migrate to under the backseat carpet and start to stink too.

I would not remove the plug under the battery I would drill a small weep hole
In the plug.

Use the search forums link up top and search Water in car Water in battery well. There will many posts on how to find the leak which is easy and how to fix it.

The really bad thing the hatch leak does is sometimes it drips right on the power plug for the hybrid battery cooling fan. It rots out that connector then fan won’t spin and car throws a red triangle and won’t start.
I would investigate that it’s easy to get too just take the passenger side cover off. Many pictures ofthat plug search for it.

 

12.4 and holding check it in an hour see what you got That's starting to head down there but it is above 12 and the car will sure keep it above that when it's running it's when it's off and yes that freezing in the wheel well or sitting half in the water and cold close to freezing whatever is definitely not a good situation for that yuasa. I have their AGM batteries and all my power sports equipment I think it's the micron something another

 

Did this shop originally sell you the battery?