Battery tender for not driving car for 1.5 months

Yes.
But it should easily survive 6 weeks with nothing extra attached.
An overnight charge before leaving and immediately upon return would be a good idea though.

AND.....the models with a 2 to 4 amp capacity are a bit more
versatile as they will charge a "flat" battery faster.

 

Does not list cars? very strange.

Reviews are good, so that does say something, if they are real reviews.

The basic charger I have is 1.2amp i.e. 1200mah had it for a few years, from amazon
I use it on all my prius batts, including my newer Prime.
Today before I put it on my Prime, the batt tested 12.2v so I keep it tethered on the weekends or longer rests.
I am more concerned about the Prime battery than previous Prius.

 

Syl, we don't actually know the draw on the 12v battery both when the car is plugged in (it has a higher draw with the electronics monitoring that) and when the car is unplugged. So, we can't really say how much charge capacity is enough. 0.8 amps is meager, probably OK, but you might think of stepping up to the next higher level. Do leave the traction battery less than fully charged and unplugged. Battery Tender brand is one of several good brands of battery maintainer.

 

I would kick it up a notch. Prime Owner's Manual:



I'm using a CTEK 4.3 (4.3 amp) smart charger, that goes through a charging regimen, then falls back to low-level maintenance charging. There's various similar chargers on the market. I'd definetely use such a charger for duration of your trip. Or at least disconnect the battery before you go.

 

Yes. On most any car.
It doesn't take much to maintain an already charged battery.

 

It should be fine. No matter how long you drive the car, PP never fully charges the 12v battery. It always has some more room. Even if fully charged, the charger you connected might be just float-charging to maintain the full charge. I looked at the link you posted. It is a fully automatic (a.k.a. "smart") battery tender rather than a very cheap trickle charger, so it should not overcharge.

 

If you are concerned, you should disconnect the ground cable of the battery as recommended in the manual. But, to be honest, I have never done that myself when I recharged the 12v battery. If you do that, then there are a few precautions mentioned in the manual. Also, you may have to re-initialize a few items like power windows and parking sensors on the car.

Below is copied from the manual
●If recharging with the 12-volt battery installed on the vehicle, be sure to disconnect the ground cable.

■After recharging/reconnecting the 12-volt battery
●Unlocking the doors using the smart key system may not be possible immediately after reconnecting the 12-volt battery. If this happens, use the wireless remote control or the mechanical key to lock/unlock the doors.
●Start the hybrid system with the power switch in ACCESSORY mode. The hybrid system may not start with the power switch turned off. However, the hybrid system will operate normally from the second attempt.
●The power switch mode is recorded by the vehicle. If the 12-volt battery is reconnected, the vehicle will return the power switch mode to the status it was in before the 12-volt battery was disconnected. Make sure to turn off the power before disconnect the 12-volt battery. Take extra care when connecting the 12-volt battery if the power switch mode prior to discharge is unknown.
If the system will not start even after multiple attempts at all methods above, contact your Toyota dealer.

 

No, I have never used Battery Tender brand charger/maintainer. I don't know what the indicator means, but assuming solid amber is the bulk charge, flashing green is the floating, and solid green is the maintainer mode (fully charged), the indicator means that it has not finished the bulk charge phase. Depending on the level of SoC on the 12v battery at the beginning, with a 0.8A which is very small, it may take overnight to get the 12v battery fully charged. Just for a reference, when I charged my PP's 12v battery from 12.4v using my 5Amp Victron automatic charger, it still took at least 2-3 hours of bulk charge to get it up to a full charged level of 13.4v.

The graph below shows the 12v battery voltage reading during the charge session on my 2020 PP using 5Amp Victron automatic charger. Started at 14:00 and the bulk charge phase did not finish until ~17:00. Then it took another 4.5hours of absorption phase charge before going into reconditioning phase and then float and maintain/storage phases.

 

+1. My 12V went flat recently and I initially attached the charger to the bracket hardware around the terminals. When the charger indicated fully charged, the 12V battery was still flat, so I removed the negative terminal hardware bracket and attached the charger directly on the battery post. This time the battery took a full charge and has been good since. Still puzzled by the entire incident, but happy to have my original 2016 battery back in operation. Upon reconnecting the negative cable, I believe the only thing I had to do was reset the clock/calendar.

 

NO. Not unless it does not show "green" after 12 hours or so.
Then THAT could be a sign that the battery is getting weak and is near to needing a replacement.
It is not at all unusual for it to take a LONG time to charge up that last 10% or so.
Future sessions might go a lot quicker.

 

It is not unusual for a totally DEAD battery to confuse a smart battery maintainer.
AND disconnecting the cable probably was just a coincidence.

Just reconnecting the charger probably would have gotten things going.
Sometimes connecting the cables to the battery FIRST and then plugging into the wall last helps.
That is actually recommended in the INSTRUCTIONS that come with some chargers.

Having said that, some models of battery maintainers just will NOT activate on a dead battery and you need to give it a shot of charge with a "manual" charger or a jump from another battery first.

 

Yeah same story here; ours is on a charger 90% of the time, and there's no way I'd be disconnecting the battery for every charge session. I use a quick-connect, so no alligator clamps, but the clamps are ok if you're careful, and it's just a once-in-a-blue-moon thing.

 

"Full charge" can have different definitions. The voltage the Prime maintains might be less than 12.0 volts, and it runs for years that way. That's OK. A nominal 12 volt lead acid battery is 100% charged at 12.7 volts, and that is OK. A charger probably puts 14 volts into the charge to get it into the battery, then levels out at 13-something volts, and that's OK.

Sam's post #16 above makes an important point. Modern electronically controlled battery chargers need some voltage from the battery to start their electronics. On a completely dead battery the charger won't start. This battery may not be junk, but people who don't know will replace it.

See the circles on the top of the battery with the + indentations? Those are caps where distilled water can be added to make up for the water that vaporizes off. The + things are just the right size for a 100 yen coin held in pliers to unscrew the cap. A 25¢ coin works just as well. Once a year or so wipe the top of the battery clean, remove the caps, look at the electrolyte levels, and add water up to the indicator inside if needed.

 

No there is only one real definition.
Full is full.
12.0 volts is about 50% discharged and that is NOT OK.
Because a conventional wet cell battery will sulfate if left like that very long.
NO vehicle is designed to leave it at 12.0 on purpose.