Replace OEM 12V battery with Group 25 AGM

If you want an OEM replacement battery without any modifications, please use batteries listed in this thread. 12V battery List | PriusChat Otherwise, read on.

This is how I upgrade the stock battery to a more powerful group 25 AGM battery.

Parts needed are as followed
Group 25 AGM battery - The one I got is Rural King RK-AGM25 (Exide rebrand)


Positive terminal - I bought 90982-05054 It is the closest match to the original Prius terminal in SAE size and it is the latest revision.


Ground cable - I bought Everstart LF15-4-77 4-Gauge Top Post Battery Cable, 15-Inches - Walmart.com because it’s inexpensive and kind of looks like original ground cable.




Vent tube - All Exide AGM batteries i’ve seen use BMW standard vents and will not work with the Prius OEM vent tube. If your battery didn’t come with any vent elbow, you can purchase the Dorman 924-254 vent kit. My battery came with the vent elbow but no vent tube. I went to homedepot bought a ¼ ID vinyl tube


Now I got all my parts, the work begins.

I placed a battery charger on the jump start terminal under the hood so I won’t lose any memory settings of the car.



I removed the trunk panels to gain access to the 12V battery.


I remove the fusible link from the positive terminal and placed it in a work glove to prevent accidental short.


I removed the battery hold down bar, the ground cable, vent tube, stock battery with the positive terminal still attached, and the battery tray.


I measured the provision screw holes to determine where to drill the new hole on the battery tray.


I drill a new hole ½” left of the right hole.


I remount the battery tray to the floorboard 1.5” away from the original spot.


I place the new battery in the battery tray.



I attach the new ground cable and the new positive terminal, the fusible link to positive terminal, vent tube and mounted the battery hold down bar.


Lastly, I disconnect the charger from the jump start terminal under the hood. The whole process took about 30 minutes.

 

So I took apart the battery mount to see if I can put a larger battery. To my surprise, Toyota made it possible to mount the battery tray in a way that increases the depth by 1.5” with little modification. The total depth after modification is 7" deep. I did a dry mount just to see if it actually work.



I set out to look for batteries that will take advantage of the extra space. I measured the maximum dimension of the new battery space and came up with 9.5”L 7.75”H and 7”D. The stock battery is about 9.375”L 7.75”H and 4.875”D.

While searching for infos on the OEM battery, I came across this page I determined D23R will take advantage of the extra space.

After looking through CAT battery catalog I found group 25 to be the direct replacement for D23R and group 35 to be the direct replacement for D23L. I also looked through this page and found group 22F, 47, 72, 75 and 86 to also physically fit but either slight oversized or undersized or wrong post orientation. Group 25 is the best fit of all the groups.

------------------Here are some of the reasons why you might consider using a larger size battery.------------------
1 You’ve installed a powerful inverter
2 You’ve installed a High power stereo system
3 You want longer radio listing on ACC while waiting in the parking lot.
4 You can get a much more powerful battery at similar cost as OEM battery
5 You get fresher batteries with shorter time on the shelf than OEM battery

------------------Things to consider when choosing your battery.------------------

Type, Safety and Cost.
Due to the location of the Prius battery (inside the cabin and next to the rear quarter panel), any kind of moderate to severe rear end accident will most likely puncture the battery case. The Prius requires a 12V battery that will not spill any liquid if punctured. With spill proof as a requirement, a wet cell battery is eliminated as a possible replacement battery. The alternative battery must be spill proof. The only spill proof battery is either gel cell or AGM. This is why OEM battery is significantly more expensive than other car batteries.
Traditional lead-acid battery is not recommended for the Prius. You don’t want to get this all over your interior in an accident http://share.gifyoutube.com/yoMPa4.gif


------------------To Vent Or Not To Vent------------------
OEM battery has a vent tubes in place to exhaust hydrogen gas out of the cabin. Unfortunately, a lot of AGM batteries don’t have vent hole readily accessible to install the vent tube.

Things to consider when using batteries without vent attachments.

1 AGM battery produces little or no hydrogen gas during normal operation.
2 The Prius battery is located between the HV Battery exhaust and exhaust vent on the rear quarter panel. HV fan should exhaust any gases out of the car or disburse into the cabin.
3 Unvented hydrogen exhausted from the battery would have risen to the ceiling and away from the battery.
4 Many AGM batteries are recombinant in that any gases created during the charging process will recombine internally. Out gassing will only occur in the event of overheating or overcharging. They can be installed in the passenger compartment or trunk space of any vehicle for this reason.

------------------Batteries with vents.------------------

Almost all of the Exide Edge AGM batteries and its rebranded counterparts have BMW vent holes on each side regardless of battery group. Group 47 from any brands also has vent attachments because it’s made for BMWs. The downside of using group 47 is that its terminal is reversed and the posts are recessed.

More Info Coming

 

The battery I went with is RuralKing RK-AGM25 (Exide rebrand) because it’s inexpensive.
Here are a few pictures for comparison with OEM battery. It is about ⅛” taller, ⅜” narrower and 1.5” deeper. I was a bit disappointed that the battery has been sitting on the shelf for about 4 months. When I received the battery, it was sitting at about 12.65V. I charged it for 3 hours at 15A auto setting then trickle charge at 2A auto for 8 hours. This brought up the voltage to just over 13V.


Replacing the stock JIS terminal to standard SAE terminals.

ELearnAid has an Install kit consist of aftermarket positive terminal and ground cable and installation instruction. http://www.elearnaid.com/pakitforinop.html

If you insist on using Toyota OEM terminal, use 90982-05054. It is the closest match to the Prius terminal in SAE size and it is also the latest revision. You can also use these parts as well for positive terminal.

90982-05030 Nut on left side
90982-05035 Nut on right side
90982-05037 Nut on left side
90982-05051
90982-05054 Closest match to the original Prius terminal in SAE size with nut on same side and it is the latest revision.

90982-05056 Closest match to the original Prius terminal in SAE size with nut on left side and it is the latest revision.


OEM ground terminal - requires a 4 AWG ground cable with ring terminals at both end.
90982-06022 Nut on right side
90982-06024 Nut on left side
90982-06056
90982-06059 Nut on left side
90982-06070 Nut on right side

OEM Ground cable with SAE terminal.

82123-47010 2001-2003 Prius OEM SAE ground cable as seen here

Aftermarket ground cable with SAE terminal at Walmart. It’s inexpensive and kind of looks like original ground cable.

Mounting the battery.

Clearance around the battery.

 

Other possible batteries that will fit.
List coming soon.

Installing reverse post battery. 2 ways to install reverse post battery. One, keeping positive post on the same side like this guy. You'll need to make an extension like him. The problem is that the battery cover has a support leg that occupy the same area as the extension would be. You can cut the leg on the red circle to get clearance.

Second way is to mount normally with the posts reversed. You shouldn't have any problem with the ground post. You'll need to extend the OEM positive wire to the fusible link. The Positive terminal will mount close to the metal wall by the brake lights.

 

I have JBL system with Safety Connect and self parking. I would need to make switches for too many components and I would have to cut wires. If you got a basic radio then 1 switch should work.

I didn't list battery performance specs because I don't think it's as important as dimension specs for this mod. There are so many batteries out there that their performance specs don't mean anything if it doesn't fit.

I think the first question you have to ask yourself before choosing an alternative battery is how important venting is to you.

If vent is important to you, then you're choice is pretty limited to Exide Edge AGM and its rebranded cousins such as Bosch Platinum AGM and Rural King AGM. The specs for those batteries are readily available on the web. Pepboys has a 25% off promo code for their batteries including the Bosh AGM til the end of the year.

Many AGM battery manufacturers have designed their batteries to work inside the cabin without vent.

If you're OK without vents, you'll have more batteries to choose from, including the most powerful one from Odyssey. Odyssey Group 25
Reserve Capacity Minutes 130
20Hr Nominal Capacity (Ah) 65

 

Do you have pictures of your installation?
Edit: Well, It was good while it lasted. Rural King has stopped shipping batteries for online orders. Their AGM batteries are in store only now. This may change in the future though.

 

That battery kit is listed on post 3. Elearnaid put together that battery kit for using Group 51 yellow tops before Optima released the Prius battery in the US.

 

The vent kit was the last resort if the battery didn't come with the vent elbow. My battery came with the elbows but no tube. I didn't want to hack up the OEM tube so I bought new tubes. As for the duct tape at the floor vent hole, I lost the OEM vent tube grommet when I did my plugin conversion.

Just wondering if there are any MPG improvements now that the ICE shuts down more often?