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

If you plan to attach an inverter, I recommend looking closely at the battery positive clamp, which includes a fuse (probably an oddly shaped fuse that drapes over the edge of the battery, if it is like the US model). The battery post clamp is one end of that fuse, and the cable to the rest of the car attaches at the other end, by a simple bolt or nut.

I recommend making your inverter connection at the cable end, simply using a ring terminal on your added cable and adding it under the bolt/nut. That has two benefits: it gives you some protection from fault current from the battery, and it makes the normal path of power to your inverter one fuse shorter, because you will normally have the car in READY to use your inverter, and the power then is coming over that cable from the front of the car. (There remains a fuse at the front end, so you are not unprotected from either end.)

Further discussion about that is here and in subsequent posts on that thread.

 

Thanks, yes, I'm very interested in adding the inverter. I have a pretty good one, heavy guage wiring, inline breaker (80A I think). I'll check your link to the other discussion...

 

Regarding the adapter you linked, it looks like one still needs to make some modifications: 1) The holes in the flag terminal is too small for the bolt; 2) Isn't the post too large for the JIS connector? Another way for the connection is to use batteries with internal threads, which both @PriusCamper and @ConcreteJimmy talked about in details in that thread.

 

Perhaps either of theses?
3217-0006 Odyssey SAE Battery Terminal Adapter Kit
Flag to Post Battery Terminal Adapters | L to Round Terminal

 

Yes, as for the bolt screwing into the U1 connector, some people online said that. I was thinking I'd just get a smaller threaded bolt at the hardware store if that happens. I'm still humming and hawing about whether to try for a 55AH, go with a mobility 50AH/45AH or... heaven forbid, get the $240 OEM 45AH vented battery from my Toyota dealer. The reason the 35AH U1 battery is appealing, beyond the $65 price, is that if I find MPG is poor or it's dead after 4 weeks, I use the small battery for other projects - and go get the more expensive 45 or 55 AH battery.

 

Thanks, yes, I think I bought the second one. As Prius II@C notes, I might have to get additional smaller thread screws. I do hope the SAE posts fit the Prius clamp terminals!

 

I don't know much about the battery terminal bolts. Is there any special requirement to prevent long term corrosion, such as SST or zinc coating? What about electrical conductivity?

BTW, regarding 35AH battery, @milkman44 did state that he had SKS and the battery performed fine after 4 years of usage.

 

Great to hear on the 35AH vs the OEM 45AH. I also saw that PriusCamper said there are no issues with an unvented battery (and it's possible to jerry-rig venting). I wonder about MPG with a smaller aux battery. On the other hand it's only 22% smaller and the amount of times the engine is going to come on, specifically because of aux 12v voltage are probably pretty small - as long as the battery holds a charge. My old OEM battery (probably very old) doesn't hold a charge well, which may be contributing to my poor (40.0 or so) MPG on short trips where the car starts in freezing weather, is driven with a bad aux battery for a while and then parked overnight until the process repeats again. It's also winter here, so the heater is on, with headlights on, due to shorter days. I did repair my HV battery pack, so would question that too as a source of bad MPG, except that it got a good grade when I tested the rebuilt pack with Dr Prius's paid app.

 

Combining cold weather and short trip will deteriorate MPG surely. In terms of battery size effect, maybe @PriusCamper can provide some insight with his MPG with the OEM battery vs 55AH battery.

 

yep... Covid makes for really bad MPG...

As for 55AH I don't think it makes any difference MPG wise. The main benefits in my opinion are 1) If you screw up and leave your interior lights or headlights on, you'll have more time to realize it before you're stranded, and 2) It's going to last longer...

It's finally time to replace my 12v that I bought around the time this thread began. I put my new 12 in January 2013, so I got many years from it.

This all for a 12v that cost me $110

 

COVID now attacks prius FE, talk about mutation.

 

Wow, what a battery! Hope you will set a record!

 

For those who can't stand the horrific carnage of failed electron circuits, we prefer to speak of its relationship with the war on Covid in more polite terms, aka:collateral damage...

 

That's pretty good for an AGM battery and, per what I read here, very good for a Prius battery.

For what it's worth, some cars have desulfating circuitry (or something else that I don't know about) built into the car-- essentially pulses applied right at the battery terminals to help keep the sulfation crud from sticking to the plates. My dad's Volvo 960's battery went something like 10 years - an outrageously long time, and other makes do this too.

Defsulfation can take many months, or at least weeks. I've got a unit like this hooked across my dying OEM 45AH Toyota battery. So far, no progress in 3 weeks that I can see. If you have a middle-aged battery, might be good to get one of these (set them on the battery and forget them) or use a plug-in 'battery tender plus' type device that desulfates as it trickle charges: (turn your ad-blocker off if there is no image/link below)

 

Is this the third battery on your 2004 Prius? How long did each battery last?

 

Yes. A 35 AH battery is smaller, but not that much.

 

Certainly a little simpler, but not as creative, and definitely not cheaper. Isn't it less important to save the money than to beat Toyota (and others) at their game of charging a much much higher price for a modestly larger battery that our collective experience says doesn't necessarily last longer?

 

Well said. Could you please elaborate how to fit the vent tube and the terminals, possibly with pictures?

 

For vent;
1) Find small plastic tube and same diameter drill bit;
2) Remove vent cover, find lengthwise location between cell caps and along the existing vent passage between caps;
3) Drill hole through cover there, and insert the snug-fitting tube so its end is in the vent passage. DO NOT drill into a vent cap!
4) Connect other end of tube to existing vent outlet hose;
5) Seal edges of cover (including the original outlet holes) with packing tape.

For the terminals, I simply tightened the existing clamps down directly on the flag terminals. I checked and retightened bolts later until things stabilized. It ain't pretty, but works well with the relatively low current required to boot up a Prius, and is reversible, if necessary. There are probably more elegant ways.

 

Thanks.