2004 traction battery says "sayonara" at 316,000 miles

Returned home from 8 day vacation and had the following error codes immediately after starting up my '04:

P3009 (HV System Short) with sub codes 526 and 612 (HV battery); C1310 (HV System Malfunction)

Checked everything per my Toyota shop manuals. Luscious Garage advice on basic isolation steps for these error codes confirmed what I thought I'd already knew, thanks Carolyn!

System relays measure open to 100 M ohms, all other resistance measurements are fine as well.
The battery, however, is hanging on to a stray voltage: negative terminal to metal case is 100v, positive terminal to case is about 30v, voltage between the terminals is about 66.
I repeatedly tried to discharge these voltages with a few light bulbs. Never lit the bulbs so I'm guessing that it's low current from an electrolyte leak between one or more cells and that case, which is supposed to be completely isolated from the battery....
All connectors are removed from the battery ECU, and battery connectors are removed from the system master relay contacts.

I'm buying a new battery from my dealer, whose on-line price is about $1600.00 with core exchange.

Any thoughts or comments are welcomed, however, I plan to get the Toyota OEM replacement since it's now competitive with after-market replacement prices.
Many thanks: this is far and away the best forum on Prius, with many well informed members, and has benefited me greatly.

 

thanks to all of you who've replied. I will post updates and plan to order the battery today.
Skibob, I think the actual price is $1699.70 after core trade in.
Bisco, I agree with you about OEM parts, more money but utterly reliable.
(Speed Racer was aired in Philly where I grew up: loved that show!)

ericbecky, thanks for mentioning a torque wrench, I do own one. You raised a question for me though: I am aware that the OEM battery is not a "drop in" assembly and I'll transfer the ECU and probably relays to the replacement unit. Do you have a short-list of everything that I'll need to migrate to the new unit? I might as well take photos and then start removing the parts needed for the replacement.
Thanks again

 

An Update: It's not the battery (yet).
I removed and disassembled the HV battery, discovered a lot of "fuzz" growing on the individual terminal connections. The copper bus bars were black. Completely disassembled and cleaned each set of terminals and associated nuts.
Removed individual bus bar links and cleaned in hydrochloric acid, followed by a dip in some sodium bicarbonate and water to neutralize acid, followed by a dip and thorough rinse in water. Once re assembled, I had no HV leakage code (or any others).

Also removed and cleaned the battery blower unit....

However, I'd noticed a connector high up in the right rear quarter panel section with some corrosion on the plastic body, plus the relay for the battery blower was wet, plus there was water on the top of the battery exhaust duct and scattered puddles by the left and right rear floor areas.
Opened connector and cleaned it, read up on water leaks in the Gen2 Prius, and went for a test drive. At about 38 miles I got hybrid system warnings and headed for home. Long story short the fan blower voltage passes through that connector. One of the wires must have been corroded almost completely away where it's crimped to the terminal. My cleaning finished it off and I traveled for about 38 miles without a blower. Last 5 miles or so I could feel the drive system getting a little rough due to battery overheating (though that code never set).
Back out driving today, will keep you all posted.

Question: one PriusChat member gave a seemingly good procedure to seal the leaky welded seams using a marine type silicone caulk. Any personal success (or failure) stories about sealing the seams will be appreciated. Thanks.

 

Another Update:
Have had some good results using the Permatex 81730 windshield sealer ("flow-able silicone") recommended by several Prius Chat members. I can only echo their advice: the surface needs to be clean and dry, then the silicone sticks well.
A garden hose can be positioned, with painter's tape, plastic wedges, etc to direct water into those drain channels formed into the hatch and roof area's metal work, thus eliminating the need for an assistant.
(My wife is a good sport when help is needed, but had lots of gardening to finish, so I rigged up the hose, and worked sections of each rain gutter to determine where the leaks probably were originating.)

After a first application of the windshield sealant and 48 hrs cure time, the leaking areas were reduced, however, there were cracks I'd missed, and then re-sealed them.

Also, the tail light trim to metal areas leave some gaps I think to be too large: passenger side had water incursion only from that area after sealing cracks at or near spot weld seams, so the tail lamp areas were in-filled with RTV type aquarium sealer. I will post photos.
Meanwhile, NO error codes of any kind after 160 miles of driving. HV battery is charging in a normal predictable way once again.
Will leak test late tomorrow (otherwise rain is forecast the following day and that should tell the tale.)

Thanks to ALL forum members who gave / posted information, both in this thread and the several threads about causes and fixes for Gen 2 chassis water leaks.

 

(Final?) update: 3 hours under a lawn sprinkler's arc, plus 2 torrential downpours, and all previous leaky areas are still dry. About 500 miles into a much cleaner, dryer and more tightly connected traction battery. Here are 2 groups of pictures; first are traction battery disassembled and cleaned, second are shots of the sealed seams (Permatex windshield sealer) and tail light assemblies ( DAP 100% silicone Household Sealer ) plus the "mouse-proofing" screens (shown by 2009Prius on June 21 2010). For these I used hardware cloth and sealed entire perimeters with Lexel clear sealant.
Thanks again to everyone for information and advice.