Bigger or second aux battery?

Leave the car in Ready when you need electricity.

 

Athony I will give two answers, one for the car, one for you.

Electrically, any 12 volt battery will work, larger is better. JEGS Performance Products 10278 JEGS Trunk Mount Battery Box Kit - Free Shipping on All Orders @ JEGS
Your current battery has JIS posts, while 99% of automotive batteries have SAE posts. You may wish to swap our your current battery so the posts match. Toyota Prius 12 Volt Auxiliary Battery with install kit for 2004 + including Plug in


Now for the answer I want to give you. Toyota has placed the 12 volt battery in the passenger compartment with you and your loved ones. To best protect them you want an exteranlly vented AGM battery to prevent harmful chemicals from coming in contact with humans. This will limit your choices and increase your costs. You may wish to private message a battery expert (salesman) such as Optima_Jim.

 

It's not starting to charge the 12v, it's starting to charge the traction, adding another 12v would simply add weight to the car and fumes to the passengers, you don't want to run the stereo while in acc, won't last 5 minutes, spend your money on sound deadening and suspension tightening gizmos.
To be precise, the 12v is not running the sound system in ready, only in acc(two pushes of the start button, foot off brake).

 

you can throw a second battery in the left hand hatch compartment and run parallel wiring thru the storage area to the oem. it should satisfy all your audio needs and requires zero maintenance.

 

AGM batteries generally are sealed; thus harmful chemicals and vapors do not get out.......and do not need to be "vented".
Does anybody even MAKE a vented AGM type battery ??

I am an advocate of KISS (Keep It Simple, Silly).

See how it goes with what you have now.
Unless the new stereo is HUGE, there might not be a problem at all.......as long as you don't run it much with the car "off".
Next would be putting in a replacement battery with a higher capacity, staying with the OEM AGM type.

If you really need more battery capacity than that, maybe you should consider that you need to scale back the power requirements for your sound system, seriously.

 

The Toyota OE, The Exide, and the Optima yellow-top are all vented AGM batteries. NO battery is sealed. There is a pressure release valve that bleeds off pressure that may (however rarely) develop under harsh conditions (e.g. too fast a charging rate) so as to avoid bursting the battery case. Our Prii batteries have vent holes and tubes to pass any released vapors out of the passenger area,

JeffD

 

That is not a vent in the conventional sense.
It is more like a safety release discharge hose.
It is an important point though and I didn't know that before.

P.S. Things like water heaters, boilers and car radiators also have pressure relief valves but they still are
considered to be "sealed" systems.