I had to jump my 12v battery today - How do I maintain a healthy battery?

I did indeed take it into the dealer.(of course the battery was once again dead the morning of my service appointment). My 6 month service was due and I asked them to check the battery while it was at the dealership. Turns out the battery was indeed bad and it has been replaced. Thank you dealership

While I was there, I did ask them if there was a way to put the car in some sort of sleep mode which would keep any of the background processes from running and sadly, the answer was no. The only suggestion the master mechanic had was to store the key fobs some distance away from the car, but there was no real definition of far away was sufficient.

 

You can disable the key fob in order to reduce the car from wasting energy trying to detect the key. While holding the lock button, press the unlock button twice and release both button. Car will lock and red light will blink two times quickly then another two times quickly. This puts the key fob into "Sleep mode", not the car, but it should help if you keep the fob within sensing distance of the car.

I had my car at an airport parking lot for 6 days and no issues for me, but I didn't measure the 12 volt battery.

 

So, is the consensus not to leave the battery connected to a smart charger when not in use - say for a month?

 

I’m bucking that trend.

 

How does one "wake up" the keyfob? Just normal use? I have tried wrapping a key in aluminum foil and it seems to "hide" the key from the car. Even when directly beside the car, it doesn't unlock like normal.

 

I'm specifically referring to the 12V battery on a non-Prime Prius - so, you have no issues leaving it on a smart charger indefinitely? I'm going to be gone for six weeks and was going to leave it on a Battery Tender until I waded through this thread and now have mixed feeling about doing so.

 

For 6 weeks I’d also consider just disconnecting the negative cable. Yeah, we did a drive today, believe it’s been 2 weeks, steady on the charger. A CTEK FWIW.

 

To wake the keyfob, just press any buttons. Before you wake it, you can verify the fob is disabled by trying to start the vehicle. If the vehicle does not detect the keyfob, then the fob is in "sleep" mode.

 

If you have a garage, there is no need to disconnect the battery, which could be bad for the car, as it cannot do the routine daily EVAP checks etc. A Noco Genius will take care of it. You can buy the cheap, 1-ampere one.

A Noco Genius will also take care of the OP’s and any other’s issues.

 

When I left my Noco Genius (5-ampere version) hooked up to my car for a month this summer, I also recorded the voltage as a function of time through the BM2 battery monitor. I was going to post it here, but I forgot, and now, the data is gone. Basically, it is three days off and two days on, repeating periodically. When it is on, it finishes with a long small-constant-current charge phase, which is why it takes almost two days.

BM2 battery monitor on Amazon

It is also good practice to hook up the Noco Genius every couple of months or so, as the Gen 4/Gen 5 12-V battery-management system (BMS), doesn’t fully charge the battery.

 

A year ago, I installed the UPlus AGM battery to replace the OEM battery which went flat in August 2024. There’s a thread in this forum regarding AGM battery in the Prius and my and other’s experience.

The AGM battery has performed flawlessly. The lowest battery morning voltage per my BM after not driving for a few days was 12.59 volts. Typically the first start of the day is 12.6X volts. I started out using the NOCO 5 to charge the battery once a month. But it takes 2 days to get the full charge experience. Currently doing the charge every 3 months or so to maximize battery life. Based on last years experience, the colder weather here results in a BMS charge voltage of 14.X volts so I most likely won’t use the NOCO to do a full charge refresh until spring.

Cheers

PS - the UPlus AGM cost me $125 which is a bargain compared to Toyota replacement sealed lead acid. So far, very impressed with this AGM battery.

Cheers

 

And it's like a Tesla. You plug it in at home to keep it charged.

 

I had a lot of trouble with the 12V battery going dead when I first got the car. I went full circle on the problem with 3 different dealers, none of which could solve the problem. My dealer blamed me for causing it. One even replaced the battery, but the problem remained.

Several trolls on this channel have claimed that I caused the problem myself, or that the problem is a bad battery. None of that is true. I have described the problem in detail, so that it might help others with the problem, or to find out if they solved it, somehow. It seems to be a persistent problem caused by high parasitic drain. My only workaround is to use a battery maintainer, which I plug in whenever I park at home. I have been living with this for 22 months.

 

I'm sure all this stuff has been hashed out already, but I seem to recall you had a wireless dash mount tach. Do you have anything plugged into your OBDC port?

 

The answer is yes, but my Bluetooth OBD2 module has a special "powersave" feature, which shuts it down when not being used.
Besides, I had battery problems long before I bought the OBD device.

 

I gave it a shot, lol.

 

I just came back from a long road trip to the west coast. Last night I made an overnight stop at a hotel that had a Level 2 charger. I kept the cooler on to preserve some perishables I had. That apparently drained both my batteries. I was unable to start the car, and my booster pack was too low to start the car also. I had to spend a few hours drinking coffee and waiting for my booster to recharge. I'm a bit disappointed that my booster pack doesn't hold a charge very well.

 

Draining it can't be too good for the 12 volt battery.

I've got a couple of Bluetti AC180 power stations that I use for stuff like running the fridge overnight in a power outage and the wood stove fan. They use LiFe batteries. I heard there's a sodium version now for cold temps. Maybe you could use one of those on a trip.

As far as lithium batteries go, they're a mystery to me. 80%, calibration, blah blah. I'm thinking some exercise is good for them. At least you'll know they work when you need them. I had an issue with a backup battery that was on low load that I kept plugged into a charger all the time. The battery lost most of its life after a year and I only found out about it when it ran out of juice after an hour during a power outage. Probably cheap and crappy unit, but the other identical one that was under a good load is still running strong.

 

So far, the OEM lead acid battery has been coming back each time.

I have a Jackery power pack, but it lacks the capacity of my 100 Ah lithium auxiliary battery, which should have gone dead without draining the main 12V battery. I'll have to investigate.

 

Nothing's easy, is my motto.