Use of UPS type 12v 45ah batteries in place of AGM automotive type batteries

People have been using wheelchair batteries in the same way, and yes it does work.

 

I used 2 7Ah UPS type batteries in parallel for few weeks when old one failed in my gen2. It worked, sort of. If car is used daily - should be fine but there are 2 things to consider:
1. not sure it does apply to gen1 but gen2 brake actuator capacitors bank is charged from 12V battery before HV battery is turned on, got brake supply fault codes when there was not enough power to do that, it use quite a lot of energy.
2. 12V inverter (14V actually) have no current limit for safe battery charging, all 100A is available if battery will decide to take it, I think it is main reason of 12V battery failure in prius. So again if car is used daily - no problem it still will be almost full next day so charging current will be safe. Thinking about simple relay in battery circuit to connect few ohm resistor in circuit when inverter is on.

 

i don't see why not

 

I haven't tried replacing the 12 V battery with a UPS-type sealed lead-acid battery. I have "jump-started" a weak 12 V battery with a 12 V, 7 Ah UPS-type SLA before, and it worked just fine. I used regular automotive jumper cables, and the biggest problem I had was getting the giant alligator clips to "bite" correctly on the 0.187" push-on terminal tabs on the UPS battery!

Most SLA batteries are not rated over the automotive temperature range. A Gen1 battery is essentially in the trunk, so it is probably as cold as "parked outside all night in Barrow, Alaska in January" on the low end, and as high as "parked outside all day in Phoenix, Arizona in August" on the high end. The importance of this is up to you.

If you want to try this, my advice would be to pick a size, and then look at Digi-Key or Mouser (US electronics component distributors) for a reference price on that battery, quantity one, from either Panasonic or Power-Sonic. There are lots and lots and lots and lots and lots and lots of brands of junk SLA batteries on the market; I've replaced many of them with one of those two brands. Also, lots and lots and lots of battery sellers on Ebay, Amazon, etc will list either the Panasonic or Power-Sonic part number in the ad, but ship a junk battery instead. Buyer beware.

Once you get a price on those two brands, Toyota's battery, or something like an Odyssey automotive AGM, may look more reasonable in comparison. When the factory 12 V battery in my '01 quit, I replaced it with the Toyota battery, including the bracket and cable kit it needed (it's physically larger than the factory part). When that replacement quit in spring 2018, I replaced it with an Odyssey AGM, rated 12 V, 28 Ah. I've been happy with it so far; ask me again in five years.

The Odyssey is physically smaller than either Toyota battery, so I had to make some shims out of biocomposite to get it to fit correctly. I also used some right-angle terminal adapters from the battery vendor to get the stock cables to fit correctly. The Odyssey comes from a factory about an hour from my house, so if I ever have to do a warranty replacement on it, I hope the vendor can just send me to the will-call window there.

At the time, Optima didn't seem to have one that can be made to fit in either size of Gen1 battery bracket. I also found some grumblings from the hot-rod and classic-car people that "old" Optimas (made in the USA) would last forever, but "newer" Optimas (made in Mexico) had quality issues. I have no idea if that's true or not; it's just what I read.

I don't work for Panasonic, Power-Sonic, Toyota, Enersys, Johnson Controls, or any other company mentioned.