AGM battery for Gen 4/Gen 5 Prius/Prius Prime and observations on the 12-V charging system

Thanks @Gokhan, got my order in for the Uplus battery and the Noco Genius 1 already arrived (same day delivery)! I thought I had read a comment here that Genius 1 is adequate, but I see that the package says that it will charge batteries up to 30Ah, and Amazon says that the battery is 50Ah. Not obvious to my why the charger would care about the ultimate capacity of the battery, but if the charger stops at 30Ah that would kind of defeat the whole point of pre-charging! What do you think, do I need to return the Genius 1 and find a neighbor who has a powerful charger that I can borrow?

[edit] According to the product page on the Noco web site, the Genius 1 can charge larger batteries but will take a long time ... 40Ah at 30 hours, 80Ah at 60 hours, 100 Ah at 75 hours. That makes more sense to me; still confusing why the package says only up to 30Ah [/edit]

 

I have a Prius Prime Premier 2017 and am seeing my auxiliary battery drain when the car has not been used for a week to ten days. Last week I could not start my car and had to trickle charge the battery. he battery is a Duralast with 480 CCA less than a year old.

Clearly I am seeing some parasitic power draw. I don't have any accessories hooked up other than the standard ones that came with the Premier. Any advice to debug the issue? Thanks.

 

Not a Prime owner, but I've been following this stuff.
Maybe you should provide some more details.
Like, the car is in an unheated garage in Boston? (If heated, could be not charging at 14.3 volts.)
How often and how far is it driven? (It takes a while to charge up the 12v battery.)
Leaving it plugged in after the battery's been topped up can drain 12v. (I think, anyway...don't have a Prime, but read about it.)
Also, if it's died a few times at this point, the battery could be on its way out already.
@Gokhan turned me onto this bluetooth battery monitor, (as well as the battery chart). Cheap, and fun, lol.

 

My car has had the battery drain in as little as 2 hours. Other times, it will start after being parked for a week. There's simply no way to predict. I have resigned myself to using a battery maintainer, and a booster pack.

I consider this to be a long-standing design flaw. It seems absurd that your car won't start when the 12V battery falls below 11.5V, when you have kilowatts of power in the hybrid battery. It looks like an intentional attempt to drive you to dealer service.

 

This is not correct. The Prius DC-DC converter will charge a deeply discharged battery at any state of charge. The term "parasitic drain" is loosely applied to the drain that occurs while the car is parked. This can be measured.

My Gen 3 had a fairly constant 50 mA drain, which would consistently drain the battery within 10 days. My Gen 5 has a highly variable and unpredictable drain, which can occur from 2 hours to a week or more. The only remedy I have found is to carry a booster pack and use a battery maintainer.

I have exhausted every avenue with dealers, including a new battery. The problem seems to be inherent with the vehicle.

 

At least the battery is easy to get to.

Hook-up an amp meter and start pulling fuses. The car should be drawing less than 50 mA when in deep sleep cycle. Keep your fob in a Fariday bag, so you don't disrupt the sleep cycle by walking your fob within range.
Most dealerships will install an aftermarket tracker; for their insurance purposes. They are usually pig-tailed off the OBD2 port power wire.

 

A Duralast with twice the OEM CCA shouldn't discharge to a NO start point in a week or two. Something else is going on.
My OEM at half the CCA regularly sits for a week or more without issues. It may be down to 11.5V, but it'll still start.....