Auxiliary 12v battery

What's IN there is a "normal" AGM type, maintenance free battery.
The abnormal parts are: the vent, the specific size, and for some models a unique type of post.

Some 3rd parties now have "exact" replacements for the various Prii models at a slightly less cost than Toyota.
I personally wouldn't have a problem putting in one without the vent.......but that might not be wise.
Otherwise, it's pretty much just a matter of making it fit.
While your at it, a little higher capacity wouldn't hurt.......if possible.

How long it lasts depends on YOUR specific environment and usage patterns.
If kept charged by driving frequently or with a small smart charger and it doesn't spend much time where it is extremely HOT, they can last for 7-8 years. Many make it over 5.

P.S. There are a LOT of existing discussions about the pro's and con's of various types of aux. 12V batteries on here already. Have you looked at them at all ??

 

To follow up on easy rider's excellent post.

Because your 12 volt battery is in the passenger compartment with humans, you want an AGM battery so as little Sulfuric acid as possible sprays around the passenger compartment in a wreck that breaks open the 12 volt battery.
Sulfuric acid - Wikipedia, the free encyclopedia

Because your 12 volt battery is in the passenger compartment with humans, you want a vented 12 volt battery so that if it emits toxic, explosive Hydrogen gas, (as lead acid batteries do when over charged) outside the car instead of inside the passenger compartment where it can accumulate.
Hydrogen - Wikipedia, the free encyclopedia


Because Toyota felt like using a 12 volt battery with JIS post rather than the more normal SAE posts, it is easiest to replace the stock 12 volt battery with a battery designed with JIS posts. Should you want to use an SAE battery Installation Kit for Optima battery in Prius

Aside from that, you want a 12 volt battery so that when the posts are close to you, Positive is on the left, and Negative is on the right, so they do not touch the metal of the car in normal use.

Many such 12 volt batteries exist for a Prius. I am not sure if they fit the c.
Optima DS46B24R Optima battery direct fit replacement for Prius 2004 + , Prius V & Plug-in Prius with Instructions

Amazon.com: Exide Edge FP-AGM51JIS Flat Plate AGM Sealed Automotive Battery: Automotive

Super Start Platinum PRIUS - Battery | O'Reilly Auto Parts

http://www.napaonline.com/Catalog/CatalogItemDetail.aspx/Battery-NAPA-Legend-75-Month/_/R-NBE9851P_0396636574

and to be honest, your Toyota dealer has a replacement 12 volt battery with a 84 month warranty that is as good as any.

 

'here' is a nebulous term if you do not fill out your location in your profile. All the sites I gave were US, if that was not 'here', not filling out your location is just wasting people's time.

 

If it was, I would not have bothered to ask you to define 'here' now would I?

You control how good of help you get. both by the information you provide, and by your attitude. Choose wisely.

 

You NEED a maintenance free battery of some kind for several reasons.
That pretty much means Gel or AGM.

Did you mean to ask about using a non-maintenance free in your original question ?
If so, don't do it. The acid fumes that leak out will corrode things and you will have to constantly check on the water level.

In addition, an AGM will last about twice as long as a conventional wet cell.
Don't be penny wise and pound foolish here.
This is NOT a good place to skimp.