Prime 12V battery upgrade. Increase size, reserve, Ah, etc.

Has anyone stuffed a bigger, better 12v battery into their Prime?

I'm about to do so in my 2017 Prime, and thought I'd see if anyone has already done it. I'll also share my research and thoughts about it. Anyone upset by long or detailed posts, you can just move along now...

Note that a lot of nice formatting via indentation got stripped out of my post, so it now looks like it was written by a 3rd grader, and you'll need to be more than a 3rd grader now to figure out the context of what thoughts are at what level of the outline. Maybe I'll try fixing that soon, maybe I won't get around to it for quite a while. I've already spent too much time on this, have other things to do today.

Size in mm, Length x Width x Height
Weight in pounds (#)
Yes, I am mixing English and Metric, for the accuracy and simplicity of whole mm versus fractional inches, both regarding actual battery sizes of different brands, and the specs of battery Group sizes.
Reserve capacity in minutes, if specified, is for 25A discharge.
Ah if specified, for 20-hour discharge at constant current
You generally get 20% more Ah than just applying math to 25A x reserve time.
Or 5/6 in the other direction. Basically, treat it as 30A having been used in reserve testing to convert.

ORIGINAL BATTERY is Group 140R, which is supposed to be 207x175x190
but the actual Yuasa battery from Toyota seems to be only 200mm long at the top, not 207mm.
The stock battery is 45Ah at 20-hour discharge rate (implying 2.25 amps)
Most batteries in this size range have about 5/6 their 20h capacity, at 25A.
So that gives 37.5Ah at 25A, or 90 minutes reserve capacity. Good for the size.

First I poked around under the hood, trying to figure out what might fit, how close I might dare to come to the hood, headlight, and other stuff under the hood. There's definitely some usable room going to waste, which is a forbidden thing to me, when going Prius Prime camping!

MAXIMUM SIZE WHICH MIGHT POSSIBLY FIT (but might not, especially if all 3 dimensions maxed)
258x225x237

LARGEST SIZE I'D PROBABLY TRY, AMBITIOUS
242x200x220

LARGEST SIZE I'D MAYBE TRY, AGGRESSIVE
255x200x230

Available Group Sizes with potential fit, correct terminal locations
Note: Some batteries are made smaller than the spec, so I consider spec sizes that don't fit.
Note: Listed largest to smallest, approximately, based upon performance of available batteries

GROUP SIZES CONSIDERED (actually there were many more, I eliminated many)

Group, size
24F 273x173x225 too long, but some companies call a 24R a 24F
24H 260x173x238 rare size to actually find for sale
24R 260x173x225 ACDelco has some 24R allegedly 255mm long which MIGHT FIT PRIME
124R 262x177x218 would need to find a short one or move something a little
22HF and 22F size OK but not very available in most brands.
35 230x175x225 No ACDelco Pro Gold in this common, POTENTIALLY GREAT SIZE FOR PRIME!
47 246x175x190 PROBABLY BUYING THIS, ACDelco 47G115
140R 207x175x190 STOCK SIZE (though I measure only 200mm long, at least at the top)

All 24F and 24R batteries I found, except one, were simply too long by a little bit.
You could move some stuff, maybe pound a piece of sheet metal or two, and they might fit.
But ACDelco has their best Group 24R battery undersized:in length to where it might fit.
ACDelco 24RPG 255x174x221 43# 130min reserve VERY TEMPTING, TO GET THAT CAPACITY
IF the advertised size isn't neglecting protrusions, etc.
Finagling or making a hidden dent for one corner, would help
Moving it a few mm up or over might help.
It would leave only about 3mm slack in length, total at both ends. TIGHT TIGHT TIGHT.
A risk to driver's side headlight in collision, but really the stock battery is a risk too.
Group 47 battery is almost a drop-in, but 35-42mm longer than the stock Prime battery:
ACDelco 47G115 242x175x190 35# 115min reserve TEMPTING FOR SIMPLICITY, CAPACITY.
(very new part #, label color scheme, supersedes seemingly identical 47PG)
There is an AGM version of the 47PG, specifically intended for the Chevy Volt.
ACDelco EVLN2 or EREV
Same size and specs, but AGM w/ 24 month warranty, vs MaintFree w/42mo warr
$200 at O'Reillys for this 24 month AGM, vs $136 for the 42 month Maintenance Free 47G115
With the Prime battery under the hood, I really don't need an AGM. Waste of money.

I found no other brands of reasonably priced batteries with the specs of the ACDelco Professional Gold 42 month batteries, available in Group sizes and physical sizes as suitable as the ACDelco choices. Except for maybe Motorcraft Max, which has similar specs in some sizes, similar prices, and a great warranty. I think almost every Group size of them which mattered was physically a little bigger than the ACDelcos, though, or had some other drawback. Worth checking out if ACDelco isn't priced well in your area. Similarly, Wal-Mart's Everstart Maxx was always close to being in the running, but never quite crossed the finish line for me, despite my having had several over the last many years, and never a complaint. I even abused one by leaving it sitting, and they didn't question the warranty exchange when it died. I remember having put the receipt in a Ziploc, inside a self-adhesive clear UPS shipping-document envelope.I put on the battery when installing it. Keep your receipt. Gluing it to the battery seems to be the best way for me to be sure I can find it.

I'd really love to jam in the ACDelco 24RPG and get that 130 minute reserve capacity over the 90 minute stock capacity. Almost 50% more than stock. But the 47PG and newer 47G115 will fit much more easily, and the improvement from the already surprisingly good 90 minute reserve of the stock Yuasa batter to 115 minutes, is still pretty compelling.

So, UNLESS SOMEONE HAS A BETTER IDEA at a reasonable price, I think I'll be getting the 47G115 for $136. As luck would have it, I recently found $50 of gift cards I got for returning a bunch of my old lead-acid batteries to them when I moved several years ago. Checked them online, still good! So I'll be $86 out of pocket plus the core charge of $18. I'll be keeping the Yuasa for garden/portable floodlight use, but I'm pretty sure I can find a dead battery kicking around somewhere to get the core charge back with.

By no means is my stock battery showing any signs of distress. I simply want to increase the reserve capacity to be able to use the 12V battery for a bit of "RV house battery" service when I it the road for some "Prius Prime camping" later this winter. At light discharge rates, I'll get an added 25 minutes of car-off power at 25A, or 6/5 that amount of energy at a small draw. That turns out to be 12.5Ah, or 150Wh. That's the amount you can draw out of a $150ish "solar generator" battery pack. So, basically it saves the space of a "solar generator" box like a Jackery 160, and gives me a bigger, better car battery "for free" compared to buying a Jackery 160 or whatever.

I've purchased a cheap backlit LCD battery monitor with loud audible alarm I can set an alarm voltage for, so I don't have to worry about draining the 12V battery if I'm hanging around or sleeping while charging/running stuff from 12V without the car Ready. Just the added 12.5Ah capacity alone will run my 50 liter freezer for longer than I sleep, without even starting to dip into the other 45Ah. And if the weather is so hot in AZ that the freezer draws more, I'd be sleeping in Ready mode for AC, and it's not a problem.

Sorry this was so long. But I did warn you.

John

2001 Prius early adopter in October 2000.
2005 Trim 6/leather still strong with 230K miles.
Running on 195/65R15 Michelin Xi3 year round
Forgot to check whether 205/65 fit it when I had them on Prime.
2017 Prime still getting broken in with 82K miles
Running on 205/70R15 96H Michelin Xi3 year round
Recommend 205/65R15XL 99H of same, year round, any climate.
Considering lift kit.

 

I've never checked my 12V voltage after letting the Prime sit unused, but I've probably let it sit for a couple of weeks during the pandemic with no ill effect noticed. It's parked far enough from the house that it's not detecting my fob and partly powering up as I move around the house.

The reason I'm adding reserve capacity is to allow using it to power things from 12V when camping and the car is completely off, not even in ACC mode. When my freezer compressor is on in (the freezer's) Eco mode, it draws about 40 watts. The average power draw with it kicking on and off, is 16 watts when the air temp is 70F and the freezer temp is 0F.

But I'll be in Arizona, in the desert where shade is hard to come by. So I will use Reflectix window covers, but the closed car in the sun will still bake. I will probably run the car in Ready overnight (starting in Charge Mode, then it will kick over to EV mode when at 80% EV range) for climate control and charging both batteries back up. During the day, I will occasionally put it in EV/Ready as needed if I'm there, drawing from the EV battery to keep the 12V battery charged despite running the freezer. . But when running the freezer (which runs 24/7) during daytime while not in the car, I'll just be draining the 12V with the car completely off, to power the freezer. The temp in the car could easily be 140F, so the average power draw could be doubled to 32W or even peg at 40W and never cycle off. Call it 2.5 amps as an example. Switching from the 90 minute reserve battery to a 115 minute reserve battery, lets me run the freezer in those adverse but not completely worst-case conditions for 5 hours away from the car, before the battery is even down to having just the stock 90 minutes of reserve left. To drain the 115 minute reserve battery from 100% to 50% would take 12.5 hours, while draining the stock battery to 50% would take only 9.8 hours. Draining a lead acid below 50% every day, or multiple times per day, starts seriously cutting into its life span. I just want to keep my frozen stuff frozen, while being able to have the car completely off and locked up, for as long as possible when away from the car hiking or whatever.

So the benefit I'll really get, is draining the 12V down to a SOC which is not as bad, or taking 115/90 times as long to reach a SOC which is equally as bad. Cheap insurance to help battery SOC, and extend battery life.

The freezer can be set to 3 different low-voltage cutoff levels. So I could choose between letting food spoil versus letting the battery drain too far. But I'd rather just go with the bigger battery, a freezer cutoff voltage that protects the battery well, and know that I have a few extra hours each day of not worrying that the freezer is about to kick off due to low voltage and start melting my food supply.

 

This is an accessories and modifications forum, and your complaint is that you don't like the idea of deviating from stock? Just because someone COULD abuse, neglect and run down both the stock battery and a much better battery, if they were neglectful enough? I'm not going to neglect or abuse anything. I just want extra reserve capacity for specific purposes I've already explained.

I think the Group 47 battery I've selected shouldn't be too offensive a modification to anyone. While trying to stuff a Group 24R (the size used in a Camry and many other Toyotas) in there would arguably be a pretty aggressive mod, the Group 47 is a well-chosen and reasonably conservative upgrade, IMHO. It has the exact terminal configuration (not just orientation, but also the same configuration of recessed and covered terminals, etc) and the exact same size in 2 of the 3 dimensions, of the stock Group 140R battery. The Group 47 spec is simply 35mm longer than Group 140R spec. There is room for that, plus about another 16mm longer battery than that, or even more if willing to bend wires out of the way or make a couple of taps on sheet metal adjacent to the battery.

Changing to Group 47 allows me to buy a battery which can draw 25 amps for 115 minutes reserve time instead of the stock 90 minutes. The most I will actually be drawing is slightly over 3 amps, and that will be intermittent. Hardly abuse or neglect.

This mod would also help people with other needs, including helping to fix the problem of drained 12V battery from sitting unused. It won't eliminate the problem, but increasing the battery capacity by 28% is nothing to sneeze at. It would mean a lot of people's cars would start rather than not start after various numbers of days sitting.

Why "stick close to the stock specs" versus put in a battery with better specs? It's not as if a better battery will be straining the car's charging system, or causing any other problems. Toyota chose the Group 140R to save weight compared to what they put in a Camry, for instance. Not due to any problem with the Prius dealing with a slightly stronger battery. I'm only going halfway up in size toward the Camry's battery size.

The battery will not be neglected. The car will be run every day. Chargers are absolutely irrelevant to me in my application. I'll be out in the wilderness, completely the opposite of what constitutes neglect: sitting unattended and the battery slowly draining without a charger while sitting next to an outlet.

If I wanted to charge it, I'd simply turn the car on. Which I will actually be doing EVERY DAY and probably most nights as well. The bigger battery is intended to simply provide several hours of 12V freezer use with more safety margin, between the times when I turn the car on. That way, I can get a full night's sleep on nights when I don't want to have it Ready all night, and I can go hiking for 6, 8, 10, or 12 hours with the car completely off and locked up, but my 12V freezer running off the 12V battery. Though I could accomplish that with an external battery pack like a Jackery, I'd rather build the battery capacity into the car, both to save space and to gain other advantages that a Jackery would not give the car.

 

Yes, and of course. I will bring a lithium jump starter along when camping.

But as far as having the watt-hour capacity to run a compressor fridge/freezer for half a day, it's inadequate and totally the wrong device for the purpose. Even if its capacity were adequate, I'd not like to be draining and charging it every day. I'll keep it charged up for its intended purpose. I won't be using the jump starter pack to charge my phones or anything like that, either. I have other USB power banks for that, which I'll charge from the car battery or solar.

Really only the car battery as-is, the car battery replaced with a better one, an extra "RV house battery", or a lithium portable power station (the most common being the Jackery brand) are suitable for my intended purpose. All of those are also suitable for hooking a portable solar panel to, to extend how long they'll keep the fridge running and/or keep the battery closer to fully charged. (Note that not all power stations allow solar charging and running loads at the same time, but I'd not buy one which doesn't, at least not for anything but a specific purpose where that's not needed.) I have a 60W folding solar panel which folds to about the size of a laptop, and a little solar charge controller, for exactly that purpose. When away from the car, with the solar panel on the dashboard, it will provide a lot less than 60W, but every little bit counts in reducing battery depletion from the freezer.

Using something like a Jackery is a perfectly fine solution, but I much prefer the car-battery solution. It gets rid of the need to remember to switch from one power source to another every time you leave or return to the car. It avoids using up the 500 charge-discharge cycles of a power station that costs around $1 per Wh of capacity. And it saves the space and expense of the power station. Whatever method you decide to use for charging the power station, can just as well be used to charge the car battery.

Being away from an AC outlet for a long time, means you're using either solar or the car to charge everything. The car is already extremely well designed for charging its own battery. Finding a portable solar panel and controller designed to charge a 12V car battery is also no problem at all. Adding another middle-man layer of yet another power-storage battery getting charged and discharged daily, just makes no sense to me. Especially when the power to charge it is coming from the car battery. Which is always, if you're not using solar. And is often, even if you use solar in addition.

 

Sounds more like a fanboy comment, than something thought through.

Optima yellow would actually be an extremely bad choice for my application. The Optima is even a bad choice in general on a Gen 4 Prius or a Prius Prime.

I see you own a Gen 3. On Gen 2 and 3, the Optima is an OK choice (though I recommend Toyota if going expensive, Duracell if going cheap, after Pep Boys stopped carrying the Bosch for it) due to lack of many other options for the funny little size of vented AGM inside the cabin on those. I do also own a Gen 2 still, and have never bought an Optima for it, but don't consider someone doing so to be a serious error or lost opportunity, as it would be to put an Optima under the hood on a Prime or Gen 4. If you can find an Optima which comes even close to the specs of my solution, I'd like to hear about it. And you can skip the marketing hand-waving about deep cycle this or that. Amp-hours speak.

There are simply any number of other batteries better suited for Prime and Gen 4 than an Optima is, regardless of cost. Several, far better. The best battery I've found for Prime, is not only far better for it than an Optima in pretty much every way, but it also costs only half as much.

I realize there's nothing sexy about choosing a rectangular black ACDelco battery, but I really don't care. I'm after battery capacity, build quality, warranty, technology, and value. And I've found a combination of those which I like. I'm paying $135.99 at O'Reillys for the slightly oversized ACDelco 47G115 battery that has 25% more Ah capacity than the even more oversized Optima yellow 35 which is $271.99 at Advance.. I'm also getting a 42 month replacement warranty instead of 36.

Optima doesn't make many sizes of batteries. They don't make the Group Size 140R (or H4 in another battery-sizing system) native to the Prius Prime and the Gen 4 Prius. Nor is it made in Group Size 47, which I've decided is by far the most desirable/reasonable size to upgrade my Prius Prime to, partly because it's one of the few Group sizes with the exact same recessed terminal configuration as 140R. While I could jam an Optima Group 35 in there, it is 35mm taller than the 140R or 47, with its non-recessed terminals therefore ending up about 1/2 inch away from the hood and protruding, instead of about 2 inches away and recessed. You could fit smaller Optimas in there, but they'd suffer even more in the performance comparison. Optima must have no interest in Gen 4 or Prime, otherwise they'd make either the size it came with, or the size I've discovered is the best size to substitute as an upgrade, and coincidentally is stock on Chevy Volt.

Slam dunk, no Optima is even seriously in the running. And even if their $272 Group 35 battery were $99, I'd rather pay $136 for the much better specs, much better fit, exactly matching terminal configuration, and slightly better warranty of the battery I'm getting.

I do sort of like the Optima's name, though, and its color reminds me of Bumblebee.

 

I totally agree. I will be carrying a Viair 88P compressor, which seems to oscillate between all sorts of different prices from $65 and $80 on Amazon...I think I'll grab it the next time I see $66, though every time it does, I feel sure it's going to be $63 or $59 soon after buying it.

But due to your above concern, and the unreliability of 12V compressors, even good ones like that, I'm also bringing a can or two of flat fix, a tire plugging kit, and last but not least a small but high quality bicycle tire hand pump. I figure that if the compressor dies, I'd not mind slowly pumping up a tire with the bicycle pump by hand, rather than driving on the rim. Slow enough to not overheat the bicycle pump. It wouldn't be any good at keeping up with a big leak or reseating a tire bead, but neither would any of the other stuff.

I've already driven my Prime about 4 miles on a totally flat and partially torn tire, without the rim touching pavement. I'd nipped a sharp granite curb, cutting the sidewall. It rolled OK with the rim sitting directly on the rubber. The flapping against the wheel well was minimized by keeping the speed to 14mph or under for the grueling 20 minute ride home to where a full sized spare and floor jack awaited. Usually I might have called and waited for a tow, but I was on my way to an aunt's funeral. Luckily I'd allowed extra time, so even after the flat tire, the limp home, the tire change, and racing to the funeral I got there only 2 minutes late, no harm done.