12v battery going flat.

[Gaz911]

I've had a few instances of my 12v Battery being too low to start the car to give the ready lights when the traction Battery is engaged and wondered why this is. 

Is it a faulty Battery? I've got a 2018 prius PHV.

Could it be due to only doing short runs to work? It's only a 5 minute drive of approx 1.6 miles. The only other things I can guess may be causing it are when I have smoking break in my car I turn it on to roll the electric windows down then turn off, then repeat this to put the window back up. Do I have to leave it in ready mode when having a break maybe? 

I've turned the courtesy light off previously in case this was draining it but it's still happening. 

Thanks in advance for any help you can offer. 

[Paul john]

If its the original Battery and lived through the covid years, change it.

[Gaz911]

It is the original as far as I'm aware. I only purchased it towards the end of 2021. Previously it was a a sales reps car and only used for longer journeys. It had 45k on it when I bought it and was used just as regularly from 2018 till 2021 as any other times so I'm unsure how the covid years would effect it? 

[Cyker]

During covid most people weren't allowed to drive so a lot of car batteries drained to the point they were damaged and lost capacity.

 

[Ancient Nerd]

Always leave the car in ready mode if you are in it. The 12 Volt battery runs down very quickly in accessory mode.

To be clear, never, ever, use accessory mode.

If you are doing mostly short journeys, get a decent Battery charger and charge the car occasionally.

To play safe, in case you forget, get a jump starter. It only needs to be a small one, but it can save a lot of grief.

[Gaz911]

1 hour ago, Cyker said:

During covid most people weren't allowed to drive so a lot of car batteries drained to the point they were damaged and lost capacity.

 

Ah OK. That wasn't the case with this car, it was in constant use

[Gaz911]

1 hour ago, Ancient Nerd said:

Always leave the car in ready mode if you are in it. The 12 Volt battery runs down very quickly in accessory mode.

To be clear, never, ever, use accessory mode.

If you are doing mostly short journeys, get a decent battery charger and charge the car occasionally.

To play safe, in case you forget, get a jump starter. It only needs to be a small one, but it can save a lot of grief.

What's accessory mode?

Maybe I didn't explain it correctly, apologies. I just open my door (using the handle only, I don't unlock using key fob) press brake pedal and start button to turn on, wind window down and turn car off. Have break (5 mins) with nothing powered on. Then repeat the above in reverse to put the window up, then exit the car and lock using key fob. 

 

 

[Gaz911]

1 hour ago, Ancient Nerd said:

Always leave the car in ready mode if you are in it. The 12 Volt battery runs down very quickly in accessory mode.

To be clear, never, ever, use accessory mode.

If you are doing mostly short journeys, get a decent battery charger and charge the car occasionally.

To play safe, in case you forget, get a jump starter. It only needs to be a small one, but it can save a lot of grief.

Yeah those jump starter things do look good. It's just the prices of a decent one. But admittedly great for exactly this problem. But if it definitely is a failing Battery wouldn't the money be better spent replacing it if I'm never going to have anymore problems that need a jump start again? 

[Ancient Nerd]

1 hour ago, Gaz911 said:

Yeah those jump starter things do look good. It's just the prices of a decent one. But admittedly great for exactly this problem. But if it definitely is a failing battery wouldn't the money be better spent replacing it if I'm never going to have anymore problems that need a jump start again? 

You don't need an expensive one. It doesn't need to do anything other than provide 12 volts at very low power to drive enough of the car electronics to switch on the main Battery.

You could even make your own with eight AA batteries. They should provide more than enough power.

[TonyHSD]

5 hours ago, Gaz911 said:

What's accessory mode?

Maybe I didn't explain it correctly, apologies. I just open my door (using the handle only, I don't unlock using key fob) press brake pedal and start button to turn on, wind window down and turn car off. Have break (5 mins) with nothing powered on. Then repeat the above in reverse to put the window up, then exit the car and lock using key fob. 

 

 

But that’s the problem when you start the car, windows down and turn off the car . After 5 min repeat the same to close the windows you are actually draining your 12v Battery. Add the fact that you only drive 5 min to your work and we have a formula for killing your Battery. 
If you start the car in ready mode you should try to keep it ON for as long as possible (20 + min) and try to avoid any unnecessary on and off situations exactly like in your example for smoking break. Your Battery is gone that’s obvious but if you replace it with new and continue to use your car  same way you will soon destroy your new battery too. You need to change how you use your car. 

[Gaz911]

On 10/30/2024 at 1:28 AM, TonyHSD said:

But that’s the problem when you start the car, windows down and turn off the car . After 5 min repeat the same to close the windows you are actually draining your 12v battery. Add the fact that you only drive 5 min to your work and we have a formula for killing your battery. 
If you start the car in ready mode you should try to keep it ON for as long as possible (20 + min) and try to avoid any unnecessary on and off situations exactly like in your example for smoking break. Your battery is gone that’s obvious but if you replace it with new and continue to use your car  same way you will soon destroy your new battery too. You need to change how you use your car. 

My thoughts too when it first happened, forum discussions said it'd be fine. Seems not. 

I'll start leaving in ready entire time see how that goes first before not being able to use my car however way I wish and how I always have done with all cars without issue

Kinda ironic, new problem affecting only new electric vehicles is related to power drain of Battery in a Battery technology vehicle. 

 

[Gaz911]

On 10/29/2024 at 9:54 PM, Ancient Nerd said:

You don't need an expensive one. It doesn't need to do anything other than provide 12 volts at very low power to drive enough of the car electronics to switch on the main battery.

You could even make your own with eight AA batteries. They should provide more than enough power.

Are AAx8 really enough to work? I know it's basically just energising a relay or coil of some kind to engage the traction Battery but no idea demand was so low

[Gaz911]

So which high level R&D senior designer / manager / engineer/ projects decided not to or overlooked the 12v Battery also charging when the traction does 

[Ancient Nerd]

18 minutes ago, Gaz911 said:

Are AAx8 really enough to work? I know it's basically just energising a relay or coil of some kind to engage the traction battery but no idea demand was so low

I haven't actually tried it, but I'd be very surprised if it doesn't work. Alkaline batteries have reasonable capacity, and you really don't need much power.

Using a jump starter on an EV or hybrid doesn't noticeably drop the state of charge.