Let's try replacing the 12v battery with a much smaller, lighter one

Great ingenuity, hope it holds up thru winter season for many years

 

Because, obviously the engineers at Toyota are just plain stupid.

Or perhaps....

They take into account the random fool who leaves the interior light on...
or the guy who leaves the car unused for a month while the SKS is searching for a key
or the guys who leave the radio on while working on the car while not in ready mode
or the guys who just leave the door open while working on the car while not in ready mode
or 10 years worth of use and degradation that still leaves enough AH to keep the car working
or a hundred other design considerations I'm sure they take into account.

Hell, a couple 6v lantern batteries would work just fine....until they don't. Then a 200 dollar battery is going to look pretty cheap compared to a 200 dollar tow + a battery and wasted time. Or the hassle involved if a wife or daughter happens to be in the car when it craps out.

 

How much labor did that cost you??
$25 a year for that battery is what it cost.
Though the car/computers don't care where the 12volts come from, it's still risky.
And they only last a few years. I've replaced many ups batteries. Unless the car battery,
they die without warning. Then you are stranded, again. Every year or two, or sooner because you
are using older used ones.
You're EXPENSIVE computers will not like that. When they demand that voltage and amperage, and it's
lower, they could burn up trying to draw the power.
It's a good idea, in a pinch. But that is something you do UNTIL you can get the correct part.

But, it's your car....

 

well done!

 

$184.93 4th of July weekend for oem battery internet order pick up same day at a local Magnussens Toyota dealer in high rent Palo Alto CA a few miles from home. This to replace the original battery that lasted eight years. Not looking to re-invent the wheel given the astonishing performance of the oem battery. They got that thing right. imho (Current price is 190.43)

 

Dude? I'm NOT a cowboy...
And the correct way to do it is to NOT do any of those things that kill the battery.
Unfortunately, people don't do that, as you know.

Rigging a ups battery with a switch that's easy to flip when/if something like this happens,
is better than being stranded. IF, you can train others to do it.

I guess your time is not valuable, but mine is. And yes, I do INVOICE my time on Prius Chat.
I send them a bill every month, and they pay it.

 

I go down these sorts of rabbit holes every so often, but less often now. Too much conjecture and loose ends in the initial premise.

What you've got in there now is essentially a knock-off version of the type of battery that comes with a JNC660 jump pack. It's "ok", but doesn't have the legs of the OEM spec battery.

 

Hi Myself248 and others. How did the experiment with the two (or one) dinky little 18AH AGM batteries go? I have an unknown age OEM battery failing now in a 16 year old Gen II car. I am running a desulfator on the OEM battery in case that helps (takes months usually) but also intrigued by the lighter, healthier battery. My MPG isn't great at the moment. I rebuilt the HV battery pack and Dr Prius gave it 102% so I don't expect the mileage is due to that battery. I do think it's due to the ICE coming on all the time to add a view volts to the 12.0 sick auxiliary battery. A smaller cheaper AGM would hold its voltage at 12.6 or wherever it should be a lot better, as long as the SKS I have won't take too much from the little battery.

 

You rebuilt the hv pack before troubleshooting the 12v battery?

 

Yes,the 12v was sick when I got it too. It’s harder to resuscitate a 12v battery than a nimh with removable modules!

Here are my HV notes, written up as a Wiki on Traction battery repair:Prius High Voltage Battery Reconditioning | PriusChat

 

I've been using a $65 35AH U1 AGM for nearly 6 years now. It works perfectly, for one-third the price. I shimmed the mounting bracket to make it fit, and adapted the battery to hook up to the original vent tube. Considering its age, I now also have a similar replacement ready. Bought the second one from Harbor Freight, using one of their 30%-off coupon.

 

Bravo! Thanks for the info. This is why we love the forums! A tiny question - I have "SKS" (the key doesn't have to be in the slot to work). Do you? PLease say yes. I've heard some complain that 'you really need a large battery if you have SKS)...

Carl

 

Another question: The 35AH U1 batteries has the flat tabs with holes in them. The Prius and all car expects "SAE posts" How did you convert the battery's tab to posts? Also, let us know how SKS works with this battery. I calculate that the battery is about 22% smaller in capacity than the OEM 45AH battery. Thanks!

 

By the time you finish cobbling changes to the hold-down bracket and cables, simpler to just use correct spec battery? Maybe even cheaper lol: and is this going to last as long?

 

CR94 writes that he's used a 35AH U1 SLA battery for 6 plus years with no issues. If the MPG stays high--engine doesn't have to come on often to recharge the aux battery and it works okay with the SKS keyless option--what's not to like? $65, some adapters from tab to SAE (I hope CR94 will enlighten us) and a shim or something to make sure the smaller battery is properly secured. The OEM battery is 3-4x the price.

BTW, my Toyota OEM aux battery registered 11.1v before I went to engage the READY mode - temperature was 10F this AM! The Prius engine with 166K, God love it, started right up, since it doesn't use the aux battery to start - and doesn't even have a traditional starter.

Of course I hope that my experiments with desulfation result in a healthy-again aux battery, but I'm thinking the 35AH $65 battery looks pretty good.

I'm eventually hoping to run 800W of inverted AC devices off the thing, as in a power outage. It would be interesting to know what the max constant current draw from CR94's smaller aux battery is.

 

While you wait for @CR94's response, there is a data point here for your reference Fitting mobility 12volt AGM battery. | Page 21 | PriusChat (@milkman44 post#412).

 

Thanks. That page (and Page 22) were helpful. I saw that someone was using the 35AH battery with SKS, I think. Also, a picture on the next page, shows a potentially good way to connect tabbed batteries to the SAE/JiS Prius connectors for pos and negative-- a large (conductive!) screw is put from the prius terminals through to the battery tab and fixed with a nut. I don't think that's as ideal as finding a good tab->SAE post adapter, but if the screw connection can carry enough current, it might be okay.

In my case I was thinking of using the prius to power an AC Inverter. I know that the safe draw (before the Inverter fuse blows!) is 100A or lower. I'd therefore prefer not to use the screw-to-tab solution, but to find tab-to-SAE post adapters, because they'll have a lot more surface area, I think.

EDIT: This is what I think we need to convert U1 tabs to SAE posts: I've ordered a pair. Flag to Post Battery Terminal Adapters | L to Round Terminal