aux. battery, questions about battery maintainer

The Noco Genius is a jump starter, and will only charge the battery, but not prevent it from discharging.

I would pick up a Battery Tender - this is a well designed charger/maintainer that you can plug into your battery (with included pigtails and a plug). It will first fully charge the battery in several phases, then will maintain that charge without overcharging the battery. I have used one every winter (4-5 months at a time) on a 2006 MX-5, and I have only the second battery in that car in 13 years. A short lead of charging cable is fastened to the car battery with ring terminals, and the plug/cap is cable tied to a nearby hose. The Battery Tender connects at the plug.

Chargers

I have the Battery Tender Plus 1.25V and it has worked flawlessly.

 

agree with jb^^^

the reason you don't want to let it sit and throw a charger on it every time before you want to drive is that the constant draining of the battery creates sulphation which is quickly killing your battery permanently.

you want to keep it topped up with a quality maintainer.

prius battery is tiny and expensive. it drains quickly when not driven regularly, compared to large camry battery. you don't want to replace any sooner than necessary.

 

We're very low usage, sometimes the car sits 3~4 days, and then might only be driven a few kms. It's garage-stored, and it has a smart charger on more than not. I wired in a quick connect (where the positive 12 volt lead comes into the fuse box), it was supplied with the charger, it's a CTEK 4.3.

Checking the second gen Owner's Manual, I see gen 2 recommended charging limit is 3.5 amps (page 420). There's also a caution to disconnect the negative battery lead. I'm a little skeptical of the need to do that, would be a big hassle if you're frequently charging. CTEK 3.3 might be a good choice for you. I've got one of those as well: easy to use, very solid, also comes with a quick connect if you want to install.

 

Was this 12.1V reading w/ IG-ON, headlights on HIGH, AC off, vent fan on high, radio on low to medium volume?
If not, that 12.1V is probably 11.5V at best. Consider getting a DVM (Digital Volt Meter) too.

Learn to apply a load for a more meaningful reading of 12V battery SOC (State of Charge).
Is my inverter coolant pump slowly failing? | PriusChat

Post #5) How to apply a load.
Post #8) State of Charge chart, AGM compatible battery chargers (which you already have).​

Yes.
Apparently Noco makes a variety of charging attachment accessories: permanent terminal connectors, cigarette plug, OBD2 plug.
GC002 Eyelet Terminal is an M6 bolt hole eyelet (1/4inch).
GC008 XL Eyelet Terminal is an M10 bolt hole eyelet (3/8inch).

No need to turn off SKS. No need to bother checking the battery strength!
Attach the eyelets (GC002 or GC008) to the battery terminal posts, connect the Noco charger, connect the 120V AC cord, walk away. The Noco Genius will automatically charge and maintain the battery, as long as it receives 120V AC. If it were me, I would probably get the XL Eyelet Terminal and connect directly to the battery posts clamps, NOT the jumper points in the engine bay.

The HV Battery may not like sitting for prolonged periods of time, especially an old HV Battery.

Actually the Noco Genius (G3500) and CTEK Mus 4.3 are pretty much indistinguishable; splitting hairs. Both are GOOD!

CTEK Mus 4.3 has a higher maximum charging output (4.3A vs 3.5A).
CTEK Mus 4.3 includes the eyelet (optional accessory for the Noco).
CTEK Mus 4.3 is just a little bit smaller in size (inches): 6.5 x 2.5 x 1.5 VS 7.6 x 2.7 x 1.9
Noco can handle more battery types (Gel Cel, Calcium, Lithium Ion), and 6V.
CTEK Mus 4.3 is 12V battery only.
BOTH handle the battery types we are accustomed to: wet lead acid, sealed lead acid "Maintenance Free", and AGM (in our Prius).
BOTH have a 5year warranty.
BOTH are IP65 (splash and dust proof), like a lot of the portable bluetooth speakers.
BOTH are spark "proof" and reverse polarity safety.
BOTH say 8 step charging. Noco lists as: Analyze, Diagnose, Recovery, Initialize, Bulk, Absorption, Optimization, Maintenance. I assume CTEK has those same steps, even though CTEK doesn't list it.
Price Advantage is Noco ($68.90 or $69.90) vs CTEK ($86.64)

CTEK Mus 4.3 is $86.64 at Amazon.
Noco Genius (G3500) is $59.95, X-Connect Eyelet (GC002) is $8.95 OR X-Connect XL Eyelet (GC008) is $9.95​

CTEK was first to the market w/ a small, smart, multiple chemistry battery charger.
Noco is second to the market as a "me too" and/or incremental "improvement" over CTEK.​

Both are solid IMO, and would make an excellent gift (bday, fathers, grad, xmas, ...)

 

Pretty much any 12 volt charger can "handle" AGM, I think. As far as I know AGM compatible just means an option to charge at slightly higher voltage. At least that's the only diff with my CTEK 4.3. You can also charge at regular, slightly lower voltage. Maybe it won't be quite as fully charged??

 

While I maintain my Optimas with a Cteks on the AGM setting, I realize my vehicles' charging systems don't "know" what type of battery is installed and will charge at whatever voltages they "want."

 

A "dumb" 12V lead acid charger will only partially charge an AGM battery due to the higher resting SOC an AGM has.
The danger is the "dumb" 12V lead acid charger can damage the AGM battery, esp if it has a high recharge rate; let say anything greater the 4Amps. A "dumb" trickle charge should be safer, but it will never fully recharge and AGM battery.

Charging An AGM Battery with A Normal Charger: It That Ok?

An AGM battery is designed to be charged slow and low, and overcharging it can kill the battery itself. So, a normal battery charger can’t be used to charge an absorbent glass mat battery.

Most of the AGM battery chargers are equipped with microprocessors that collect information from the power cell to see its current charge status and to adjust the voltage and current accordingly.

AGM Batteries Can Be Tested the Same Way As Conventional Batteries
These type of batteries can’t also be tested the same way as the conventional batteries. This is because AGM power cells have lower internal resistance compared to flooded power cells. Older versions of battery testers will not provide an accurate test result for AGM batteries.

But some of the new testers or analyzers of today are designed to have a special testing mode for AGM batteries. This allows them to accurately test or analyze an AGM battery and produce precise reading or results.
​

https://www.knowyourparts.com/technical-resources/blog/three-misconceptions-agm-batteries/

You can use your regular battery charger on AGM or gel cell batteries.

False. These batteries like to be charged slow and low. Many AGM/gel cell battery chargers have microprocessors that collect information from the battery and adjust the current and voltage accordingly. Some have different settings for charging flooded, gel and AGM batteries. Overcharging can kill these batteries. Also, alternators are not chargers. Don’t rely on an alternator to do the work of a charger. If a battery is discharged to the point that it cannot start the vehicle, use a charger as soon as possible to make sure the battery gets fully charged.

AGMs and gel cells can be tested the same way as conventional batteries.

False. These types of batteries have lower internal resistance than flooded batteries. Older capacitance battery testers/analyzers may not be able to accurately read these batteries. Most new battery analyzers have a special mode for AGM/gel cell batteries. Old-school load testers might not provide conclusive results.​

 

I will venture to guess that the 12V bus on the Prius will NOT charge at whatever voltage. The ECUs on the 12V bus probably adjust the output voltage as needed. The 12V bus won't continually put out 14V to recharge the 12V AGM battery; the output will adjust to the needs of the 12V AGM battery.