This whole thread is astonishing to me.

You guys have more patience than I do. I would be pursuing lemon law before I went through all this crap with the batteries. You must really love the car to put up with this nonsense.

Which trickle charger did you get and was it easy to install?

I have several battery maintainer/chargers. The one I use most is a BatteryMinder 128CEC. It is temperature-compensated and has different modes for different batteries as well as 2, 4, and 8 amp charging.

I also have a 1.5 amp BatteryMinder 1510, which is more affordable, but also temperature-compensated.

Temperature-compensation is rarely seen in 12v chargers, but should be more common. Lead-acid batteries are temperature sensitive, but also forgiving, which is why temperature-compensation is so rare. I've attached a chart showing the optimal voltages.

I have pigtails installed on my motorcycles, but not my automobiles, so there is nothing installed in the RX450h+, I just hook it up to the underhood charging points.

https://www.batteryminders.com/batte...er-maintainer/

https://www.batteryminders.com/1510-...-with-warranty

I got a

NOCO GENIUS5, 5A Smart Car Battery Charger, 6V and 12V Automotive Charger, Battery Maintainer, Trickle Charger, Float Charger and Desulfator for Motorcycle, ATV, Lithium and Deep Cycle Batteries

Found on Ebay for $49.95 It has 3 year warranty which Noco confirmed is ok regardless of where purchased. Also got an eyelet connector for easy connection. I just run the charge wire through the back seat window.

Not sure if it's mainly with the 450h but I've had this happen to my 350h

Thanks to both @jahnjva and @WellsB for the info on the trickle chargers. Although I don’t like it, I feel like for peace of mind, I should get a trickle charger (and possibly a booster charger in case we’re out and need a jump). That being said, I’m admittedly new to all these things related to manually maintaining a 12V Battery, so forgive the dumb questions:

1. Does the amperage, capacity, and output matter? What are minimal specs I should get for these batteries? For example: 2A, 40Ah capacity, 28W output?
2. What features are critical when buying a trickle charger? Sulfication, Temp Regulation, Auto Stop when Battery reaches threshold, etc..?
3. What is good maintenance practice for using? Weekly, Bi weekly, Once per month, etc? Don’t want to overthink this but also don’t want to be needlessly overcharging battery every week if not needed.
4. Similar to #3. What setup did you guys recommend is easiest? Direct and permanent hook ups to the 12V battery in back with easy connect? Or just use charging points in front hood? I am leaning towards permanent hookups to battery and just easy connect to outlet cord when charging?

That being said, thanks for the links. I also found this: https://a.co/d/fhdDMJA and https://a.co/d/7tI2dPL

Thanks in advance for everyone’s help.

On another Forum, a link to this Bluetooth Battery Charge Monitor was just posted:

I suspect there is sunk-cost fallacy at play for some, like me For others it might be a bit of religious devotion, to Lexus

More seriously, I found that this problem exists in the 4th Gen RX's as well, and of course for the 2nd Gen NX - reported in those respective subforums, where people installed AGM batteries to fix it for good. I'm hoping for pioneering explorers here would find a DIY solution like that and report back!

The most critical item is auto float or shutoff. The classic "trickle charger" doesn't have that, but all reputable battery-maintainers do. The more amps a charger has, the faster it will recharge a battery. 8 amps is about the most you want for the RX battery and will recharge it in about 3 hours, from around 12 volts. A 2 amp charger will take about 12 hours.

Desulphation is an interesting option. Many chargers have it, but I don't know that there is definitive proof that it works. It doesn't hurt...

I feel that temperature-compensation is important for longest battery life, but any charging with a good charger/maintainer is better than nothing.

A permanent pigtail is nice as it makes it more likely you'll charge the battery regularly, but it's not a must-have to me, except where it's difficult to get to the battery or charging terminals as it's common on motorcycles.

How often you should charge really depends on the vehicles charging system. I charge most batteries monthly, but the RX450h+ has a poor charging algorithm, so I'm charging it weekly. The battery monitor above can make it easy to track your voltage and know when to charge.

Thanks for the detailed advice. Super helpful. A few follow up questions: For longevity, is it bad to “fast charge” the 12V Battery at say 8A every time, vs “trickling” it at 2 or 4A? The chargers I like have the variable 2/4/8A options. Also, Float = Auto-Shutoff?

8 amps isn't fast charging an RX battery and won't negativity effect the battery.

Auto shutoff means the charger stops charging, usually after absorption stage. A battery maintainer will start charging again if the battery voltage falls to a certain level.

Float mode drops the voltage from around 14.4 down to around 13.4. This will finish the last 5-10% of the charge, over the course of several hours and then hold it at fully charged until it is disconnected. This is better, with a temperature-compensated float being ideal.

The manuals usually detail the charging stages of s

The basic charging stages are constant amps with voltage rising(bulk), then constant voltage with amps falling(absorption), then float(reduced voltage with amps falling off to almost nothing)

Oh I see. So it’s good to get both Float and Auto Shutoff?

It's best to have float without auto shutoff. A battery on float sees virtually no wear.

So was thinking getting this one you recommended, but didn’t see anything referencing float or auto shutoff, but assume it’s does? https://www.batteryminders.com/batte...er-maintainer/

It has float.