Sealed AGM UPS battery in a pinch

Even as we speak, there is a thread with a sealed AGM battery hissing because it is red hot, in the passenger compartment of someone's Prius.
I worry for his loved ones and I worry for yours.

12V battery dead? | PriusChat

The right battery is an investment in the lives and well being of your passengers.

 

You want a S46B24R battery

Optima DS46B24R Optima battery direct fit replacement for Prius 2004 to 2015 , Prius V & Plug-in Prius with Instructions

Exide AGM Car Battery (Group S46B24R)

http://shop.advanceautoparts.com/p/autocraft-platinum-agm-battery-410-cca-s46b24r/

AGM Toyota Prius Auxiliary Battery - Made in the USA: BatteryMart.com

and many more.

These batteries are vented, (there is tubing in the Prius to vent out side the car) AGM batteries with JIS posts rather than the usual SAE posts, so replacement is both safe and easy, if not cheap.

 

• The 7.5 Ah battery might work in a pinch, but would be too small to last long.
•On another hand, a sufficiently larger "sealed" general-purpose (used for UPS and many other purposes) 12V AGM can be decent replacement, as long as it fits the space, is securely mounted, and is vented.
• The jumpstart thing would get you started with a failing battery, but, besides being small, is probably the wrong chemistry and voltage to coordinate long-term with the car's 12V system. I'd be afraid to leave one connected longer than necessary to boot up the car.

You surely can read a lot of silly alarmist nonsense here! All so-called "sealed" AGM batteries are designed to vent if necessary. The "red-hot" battery in the other thread is apparently the same brand and model second-most commonly recommended for Prii. Why it got hot is unclear, although we can guess.

 

8 d cells in a pinch. or a rechargeable power tool 12v battery. btw, you can buy the oem for under $200. or an optima, duracell or other may be even cheaper.

 

Ouch, sounds like you need to change your dealer! Here's my experience, I noticed that something was wrong when my SKS started acting flakey, and despite changing batteries (in both fobs) the SKS would only work when it felt like it! …and then early one morning (yup, just as the sun was rising!) when I eventually was able to get into the car (2009 Gen II) (using the hidden key in the fob - see user destruction manual p. 34) imagine my surprise when MFD lit up like Yule Tree, red triangles yellow squares, green stars etc. etc, all very pretty, but I had an inkling that something might be wrong! (I suppose the dim dome-light might have also clued me in!), so I turned to my trusty jump-starter power source (see threads passim) which I purchased from BatteryMart.com, and got the Prius to "Ready" and off we went! The jump-starter is about the size of a paper-back-book, and I've used it a number of times to get other folk out of trouble (without having to risk the sensitive electronics of my Prius) for instance when someone (damsels in distress) asks me for a jump-start! Anyway, I took the car into my local dealer and asked them to do a load test on the battery, which they did, and confirmed that it was on its last legs (never been changed so it was about 6 years old). Bill for battery was $240 which included labour and testing! (…and the work comes with dealer warranty)

 

After reading the last paragraph of your post, I can only advise you to read up as much as you can about grid charging and reconditioning your Traction Battery. Prolong Battery Systems. Extending the life of your hybrid. – Hybrid Automotive is a good place to start! Good luck!
PS: I don't work for Hybrid Automotive, athough I do use their products (…and so far (touch-wood!) my car's Traction Battery is in pretty good shape! …I just hope it stays that way!)