I suspect it's really doing a CA test, unless you have a 0 ℉ freezer to keep the battery in for a while before testing, or you make sure to use it on winter days that happen to be 0 ℉, which would match an official CCA test. Or maybe the reduction in CA with decreasing temperature has a known formula, and the tester measures the ambient temperature and corrects it to 0 ℉ with math. I don't know if that's practical.
It has several other options, including CA (Crsnking Amps) though I’m not sure my battery specs that. Would there be a general factor applicable to CCA that would ballpark the CA? that said, testers of that ilk typically offer CCA measurement; they employ some method to make measurements at other than zero?
I wonder why you care about crank amps for a Prius? The 12V does not crank anything, it just powers up the ECU… Yuasa is the best I have tried, but I also use ctek attachment and recond them 12V every quarter year regardless. Dead aux batteries are the worst.
That's not the first time that's been wondered in this thread. Seems like every time it gets wondered, someone has to say again "because there are common tools that let you compare a battery's present cranking amps to the cranking amps on its label, and that's an easy way to get an indication of the battery's present condition". Doesn't need to have anything to do with 'cranking' needs of the car.
Agreed, but then I also have to wonder what do a Prius actually need in A (sustainable for five seconds?) to boot the system? (CA value is defined on need to be able to (repeatedly) crank an engine. That is a highly irrelevant value for the Prius.)
The banal ballpark test for any battery sustainability/capacity - apart from for Prius irrelevant CA - may be to know the exact A input charge, then measure the amount of time in H it takes to get that battery to full - if initially almost empty. It’s fairly obvious if a ie 45Ah battery charges very fast (under 2 hours on 5A charge) from empty/low, it’s a loss/toss. Even CTEK can’t fix those and it will not hold for any kind of weeks.
That same condition may also show up quickly on the local auto shop's CA tester, as a value much lower than what's on the label, and that's a convenient test you don't have to wait 2 hours for. As far as I know, that's the only reason PriusChat people give for caring what CA your battery's label says. Even the lowest commercially-available car battery CA ratings are several times what it takes to make a Prius READY. There are threads in this forum where graphs of amp draw during the few seconds of going READY have been posted. I seem to remember the area under the graph being about 90 amp seconds, over a stretch of 2 or 3 seconds, so an average of 30 amps or so, but the graph is more spiky than steady.
AI answer; The 12V battery only requires about 30 amps (per what tempus?) to turn on the computers, which then allows the high-voltage battery to start the car.
If the battery does not use its power to close the high voltage relays, just powering the ECUs is a moot point.
I don't think that 'news' was entailed by anything the quoted poster wrote. Yes, for the second or so before the car makes READY, the 12-volt battery powers all of the 12-volt equipment that happens to be turned on. The dash instruments, the ACC and P/POINT relays, the three IG1 relays, the IG2 and EFI and IGCT relays, the brake and power steering systems, and all the ECUs. When the power management control ECU completes its checklist and judges the car safe to go READY, that ECU then powers the three relays in the battery in their proper sequence. I've never understood why so many posts seem to fixate on it powers the high-voltage relays! as if it were somehow the main thing the 12-volt battery was doing. The total draw of all the relays I've just mentioned is probably less than the dome lights.
It's a worthwhile test of the battery's viability, regardless of the application. I test with a Solar BA5, and typically CCA is well above spec. When it's dropped, to significantly below spec, the tester gives it a fail. If I keep the battery in use under those conditions, simple voltage checks show it drifting lower, and doing so faster.
This is true if you wish to crank an engine, but bad information in my mind for any Prius battery. How do anyone define viability of a battery? Your test prioritize testing only maximal output of amps. It’s a quick test - and a way to get stranded. Many batteries will deliver this for some seconds and then they are empty. I like to use words such as sustainability since in any climate batteries will loose charge by definition - even unplugged, it’s just chemistry and mathematics. I would still like to emphasize if a battery is able to charge fast compared to input A and Ah capacity, it’s bad. It can still deliver 300 CA but will loose this over a short time.
Sounds like quantum mechanics logic, a battery can be both bad and good, depending if it's in a conventional or hybrid vehicle. Gotcha...
Great. Because that is the point. 45 Ah is a measurement unit defining 45A draw/cranking for one hour. If you can pull 300A for five seconds, how does this test the viability of the battery (if we define viability as something that will last and not just deliver 300A and then not deliver any A?)
It's a measurement unit defining a curve with hours on one axis and amps on the other and having 45 as the area under the curve. That's not quite the whole story, though, because while an idealized battery might give you that as 45 amps for one hour, or one amp for 45 hours, or 5 amps for 9 hours, a real battery will measure out a bit differently at those different rates. To have a usable standard for comparison, the time is set at 20 hours (for automotive batteries) by convention, so a 45 amp-hour battery is one you can discharge in 20 hours with a current averaging 2.25 amps. Everyone in the thread agrees that a published CA or CCA figure isn't directly relevant to starting a Prius. (The 140-amp fuse in the battery positive clamp would blow if any such current were really to flow.) That doesn't mean the figures aren't of any use, though. They are handy because of the widespread availability of battery testers built to test under those corresponding test standards. So it is easy to pull a tester off the shelf and get a current number for the battery to compare to its published CA or CCA rating. If the number has declined, that's an indication that the battery's condition has deteriorated. And the test didn't take 20 hours. If there were such things as batteries that could deteriorate substantially on that test but still be just peachy with their whole lives ahead of them at lower currents, that could be an argument that the test isn't useful. But in practice it seems that a battery whose CA performance has markedly deteriorated is a battery whose condition has deteriorated, period.
