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

Some people make up safety concerns just to clobber someone with it.
I call it "safety trolling."

 

My tentative conclusion for the variable parasitic drain had to do with the communication module downloading updates to my car's system. I measured it at up to 330 mA at times. It caused me many dead batteries before I applied my remedies.

My Gen 3 Prius had a steady parasitic drain of 50 mA. I could count on about 10 days parked before the battery was too low to start.

 

Pull the fuse for the DCM and observe any changes. That's the only communication module (that I know of) that receives power while the car is off.

Fuse is located in the driver foot well fuse box. I replaced the fuse for mine with a switch that has a mini fuse connector at the end (with each side of the switch's wires fused appropriately). This switch integrates into an empty button slot on the dash and looks oem. I turn it on when I need cabin microphone. Otherwise it stays off.

 

I gave up trying to predict when my battery went low. It was such a nuisance that I installed the battery maintainer, and I never had that problem again.

I had a Bluetooth OBD, but it drained my battery, so I deign to use one again.

 

I kept forgetting to unplug it when I parked, so I just quit using it.

 

I don't see how a battery monitor could tell me more than my clamp ammeter.

 

You need to get one to find out. The ones I have don't measure amps, but I haven’t had the need to go hall or shunt yet to get the amps reading. I may get this kind so don’t have to use a phone while driving. Just save the phone for calls while driving or looking at texts while driving.



ANCEL BM200 PRO+ 12V Battery Monitor, 433MHZ Wireless Transmission Battery Monitor with Cranking & Charging Test, Voltage & Temperature Monitoring,...

 

I don't think I'll bother. I haven't had a dead battery in over 9 months.

 

Thanks to Gokhan for the original post. My original battery died and I chose the same setup (except for the charger/tender for which I already had the CTEK MXS 5).

My OEM battery had problems starting right away with the first winter in 2022. I typically only drive the car 1-2 times a week. Now after 3.5 years it's completely dead.

Even with the new battery, I see that my voltage drops quite quickly when the car is not driven and not connected to the charger (12.91 to 12.80 in 12 hours). Anyone lese seeing this? I suspect that my Allstate Milewise device causes a significant parasitic drain.

 

Are you unplugging the traction pack once it's fully charged and/or keeping your fob in a Faraday bag when not in use?
I'm still on my OEM battery, but I don't get the frigid temperature swings that you get.

 

Don't make the mistake I made with my Gen 3. The battery ran down from parasitic drain, and then it froze. It wouldn't take a charge after driving the car for several hours. I replaced the AGM battery at great cost, and experienced the same thing with the new one, Turns out, the remedy was to bring the battery into the house and charge it fully.

 

Gosh - I wish that I had seen this tread a week ago. I replaced the factory battery in our 2017 Prius V on 18 January as we were just entering a sub-zero cold spell. The factory battery didn't owe me after 7-1/2 years of service. I did replace it with an AGM battery based upon my understanding of the technology and an impressive experience with another AGM battery.

The part that I learned here has to do with the initial charge. Suspecting that the battery could use a charge I hooked up a 4 Amp smart charger after installing it. I noticed that after 4 hours the charger wasn't reporting a full charge but i had to disconnect the charger and go about my business.

So the question is this: should I reconnect the smart charger and let it run to completion? This battery came with a 4-year full replacement warranty. The other AGM battery I have owned went eight years and showed no sings of distress when that car left the stable.

 

I bought a NOCO Genius 2 which is fully adequate, even though if I'd been paying attention, I'd have got a 5.