Charging the 12V battery in the boot

N13GEY · April 3, 2020

Anyone help? Is it OK to connect a Battery charger, directly to the terminals of that Battery in the boot of my 2009 450H?

I managed to flatten I believe that Battery when leaving the radio & doors open for a couple of hours. After reference to the handbook I junp started the car from another via removal of the engine covers and connection to the indicated terminals. It was a real faf and took a fair time to accomplish! I guess by jump starting the car in this way puts volts to the Battery in the boot? Its easer to get at that Battery, if needed, hence the question. Thanks for your help. Nigel

Vlady · April 3, 2020

Hi Nigel, a week ago I received a CTEK Battery charger and even though I did not have problems with the Battery I connected charger to the Battery which is in the boot. My intention was just re-fresh the Battery a little and recondition it, so far Battery works great, may be a placebo effect but I feel it works better then before!

I am not sure if I did right connecting directly to the Battery in the boot though but it makes sense if you want to charge the Battery you connect straight to it, however, it might be different with the Hybrid! I know I have a hybrid but I never thought it would be an issue. Sorry, probably not much help there.

johnatg · April 3, 2020

Following on from the posts in the thread I started 'Inactivity during lockdown':

You can connect a Battery charger - either a trickle charger (preferably disconnect the Battery from the car) for a very short period or much preferably a smart charger (which can be left connected to the Battery and the Battery to the car - don't forget it if you drive off though).

When you charge a Battery Lead Peroxide is formed on the + plates and the - plates become spongy lead. If you carry on charging after this process is complete the Battery will start to gas - release Hydrogen and Oxygen. You are electrolysing the Battery acid or at least the water content. The plates are not suitable for that and will be destroyed in short order.

(Electrolysis of water from renewable energy to form Hydrogen in volume is the holy grail of hydrogen fuel technology)

When a Battery discharges Lead Sulphate forms on the plates and if it is left too long in a discharged state the process becomes irreversible - the Battery is sulphated and sooner or later, scrap.

A smart charger (eg Ctek or CSI Airflow - other brands are available)) charges the Battery up to full then discharges it slightly and continues to cycle it up and down so that it stays more or less fully charged but never overcharged. It can be connected indefinitely. (The process is actually a bit more complicated - see Cteks web site - https://smartercharger.com/)

Never use a standard type fast charger on a maintenance-free (or AGM) Battery - plates reinforced with Calcium are much more prone to damage than old fashioned Antimony - reinforced batteries.

Herbie · April 3, 2020

1 hour ago, Vlady said:

I am not sure if I did right connecting directly to the battery in the boot though but it makes sense if you want to charge the battery you connect straight to it, however, it might be different with the Hybrid! I know I have a hybrid but I never thought it would be an issue

All you're doing is supplementing a dodgy 12V source by piggybacking a good 12V source onto it.

12V is still 12V, whether at the front or the back, so it makes no difference whatsoever where you connect a charger or jump leads - the main thing to worry about is making sure to get the correct polarity.

toe · April 5, 2020

On 4/3/2020 at 11:41 PM, johnatg said:

Never use a standard type fast charger on a maintenance-free (or AGM) battery - plates reinforced with Calcium are much more prone to damage than old fashioned Antimony - reinforced batteries.

Many CTeks have the AGM mode. I have used the AGM mode many times on my RX450h and GS450h and haven't seen any adverse effects (still on the same battery). Are you seeing negative effects?

johnatg · April 5, 2020

No - CTEKS are all smart chargers not fast chargers so you would expect them to be fine - as they are.

Sent from my PSP7551DUO using Tapatalk

LexIS200Sport · April 7, 2020

Here's my setup. I'm using a Maypole smart charger and a Bosch S4 sealed Battery in my GS450h.

The lamp in the boot is switched off and the bootlid is left ajar to allow for the charger mains lead to trail out.

Vlady · April 7, 2020

Do all GS's come with AGM Battery?! I charged + recond mine as a normal Battery! Ups!

Zotto · April 7, 2020

Nothing bad, it' s worse charging normal Battery with AGM settings. More, it is quite probable that GS Battery is not AGM.

Vlady · April 7, 2020

15 minutes ago, Zotto said:

Nothing bad, it' s worse charging normal battery with AGM settings. More, it is quite probable that GS battery is not AGM.

Thanks Luigi. I had to go and check what Battery I have - it is Panasonic S65D26R, I looked for a spec on it and nothing comes up that tells me if it is aAGM Battery or not, it only says Maintenance Free. I also went trough a manual and there is nothing on the type of the Battery in GS450h, weird!
My 2009 BMW had an AGM Battery even though it was not stop-start system in the car.

johnatg · April 7, 2020

I guess re charging settings you are referring to the CTEK MXS 5.0 instructions - although they have an AGM Battery setting, obviously intended to be used for AGM batteries, the instructions also say that the 'Car battery' (alone) setting is suitable for most AGM batteries. So nothing to worry about, although it might be preferable to use the AGM setting.

The Panasonic S65D26R Battery is AGM - AFAIK all Gen 4, at least, GS cars are fitted with AGM batteries as OEM - most Gen 4 GS that have not had their batteries abused (eg by standing uncharged or regularly being completely discharged) will still be on their original batteries.

AGM has nothing to do with stop/start - they are often fitted to cars with the Battery in the boot (my MK1 MX-5 had an AGM Battery from new and that was 29 years ago, well before stop start technology was common), although it is true that most cars with stop/start are fitted with AGM batteries.

Zotto · April 7, 2020

Stop start in hybrid car does not involve 12 V Battery use. AGM batteries are sometimes preferred because are long lasting and in hybrids big currents are not required while in traditional engines great currents are necessary for starting.

Vlady · April 8, 2020

16 hours ago, johnatg said:

I guess re charging settings you are referring to the CTEK MXS 5.0 instructions - although they have an AGM battery setting, obviously intended to be used for AGM batteries, the instructions also say that the 'Car battery' (alone) setting is suitable for most AGM batteries. So nothing to worry about, although it might be preferable to use the AGM setting.

The Panasonic S65D26R battery is AGM - AFAIK all Gen 4, at least, GS cars are fitted with AGM batteries as OEM - most Gen 4 GS that have not had their batteries abused (eg by standing uncharged or regularly being completely discharged) will still be on their original batteries.

AGM has nothing to do with stop/start - they are often fitted to cars with the battery in the boot (my MK1 MX-5 had an AGM battery from new and that was 29 years ago, well before stop start technology was common), although it is true that most cars with stop/start are fitted with AGM batteries.

Thanks John, well, next time I will charge it as AGM. 🙂

toe · April 13, 2020

I wouldn't charge it with the AGM mode, the normal mode is suitable for AGM. AGM mode just sends it a higher voltage which is not required.

Also AGM doesn't really last longer, it's to do with safety because there is no liquid that can leaked when your car is rear ended and is upside down, thats why all batteries in the boot is AGM.

Imagine this, someone rear ends your car, your car flips and the Battery case cracks leaking acid into your face and eyes while you're stuck inside.

ColinBarber · April 13, 2020

9 hours ago, toe said:

Also AGM doesn't really last longer

they tend to last longer in that they can tolerate a higher level of discharge without being damaged and losing capacity. The smallish capacity that Lexus fit to hybrid models means they get discharged quite heavily when left for 2+ weeks (e.g. going on holiday) and that smallish capacity gets even smaller on the flooded Battery.

LexIS200Sport · April 15, 2020

What about GS450h Sport models with the active stabiliser system? Does the second 12V Battery need trickle charging separately?

Herbie · April 15, 2020

23 minutes ago, LexIS200Sport said:

What about GS450h Sport models with the active stabiliser system? Does the second 12V battery need trickle charging separately?

There's a second 12V Battery? I didn't know that, cheers.

If that's the case then I suppose it will as all batteries self-discharge over time.

LexIS200Sport · April 15, 2020

Indeed there is - it is located in the boot in the spare wheel cavity, in exchange for the spacesaver tyre. Just wondered if the active stabiliser Battery is completely isolated when the car is switched off (unlike the main 12V battery). Then again, as you say, there is the question of self-discharge...

Attached photo is from a GS450h fitted with the active stabiliser system. The second 12V Battery can be seen in the bottom right corner.

Bit of an afterthought of an implementation (by Lexus standards) in my opinion.

Herbie · April 15, 2020

50 minutes ago, LexIS200Sport said:

Attached photo is from a GS450h fitted with the active stabiliser system. The second 12V battery can be seen in the bottom right corner

Ah right, cheers for that. So the first 12V Battery is under the bonnet I presume?

What does this second one control and which one would you connect jump leads to if they were needed?

EDIT - Sorry, just re-read your post and I see that this one is dedicated to the active stabiliser system. I'm intrigued by this - wonder why it needs its own Battery?