Fitting a larger 12 volt battery.

Britprius · November 12, 2018

I have fitted a much larger 12 volt Battery to my GS450H and these instructions should apply to other GS cars. The advantages are a much higher capacity "110 ah against 70 ah for OEM", and cold cranking amps depending on the Battery purchased of 750/800 amps. For non hybrid cars this should translate into higher cranking speeds, and faster starts. It will also be able to stand for much longer periods of inactivity.

The Battery compartment is capable of accommodating batteries up to 330 mm in length without problems against the OEM fitted Battery of 270 mm. The other Battery dimensions "width, and height" remain the same. The Battery hold down brackets, and terminals remain as OEM.

It is only the Battery tray that requires modification to accommodate the longer Battery as follows.

Remove the terminals to the Battery negative first then positive. There is a small temperature sensor on the hybrid Battery. This should be carefully pulled out of the old Battery, and stuck by whatever means you wish "glue, tape ect" on the top of the new battery

Remove the Battery and the three bolts holding the tray. The rearmost end of the tray has two spot welds on each side. First, and second picture.

Drill out these 4 spot welds at the rear of the tray only. Bend down the rear lip of the tray " i used a large adjustable spanner" till it's top edge is level with the Battery seating area, and fit a piece of edging strip. Pictures 3 and 4.

Bend up the tag on the rear lip till it is horizontal, and attach the negative lead to this with a suitable nut, and bolt. Trial fit the Battery to the tray. Picture 5.

Refit the tray and then the Battery with holding clamp. Refit the terminals fitting the positive terminal first then the negative. All the covers should fit as with the OEM Battery.

The Battery I fitted measures L 330 mm, W 172 mm, H "to top of terminals" 222 mm. It weighs 24.9 KG, and cost £80 with a 4 year guarantee.

This may be possible on some other Lexus models. Careful measuring should tell.

John.

Hangie · November 12, 2018

But why ? Especially on hybrid.

i never feel any need for a more capacity of 12v Battery. Do you have some extra accessories ?

Initial P · November 12, 2018

Never had a problem with the OEM Battery until my alternator started to fail since its been replaced the car is better than ever with a constant voltage reading on idle at 13.8v MPG has also been slightly higher since too (24 in town vs 18 old & 41 motorway vs 36 old) although I'm not sure if that where the gearbox learning driving style reset as it was disconnected from the Battery for 3 days.

Northern_Si · November 13, 2018

21 hours ago, Hangie said:

But why ? Especially on hybrid.

i never feel any need for a more capacity of 12v battery. Do you have some extra accessories ?

My understanding is that the 12v Battery on the hybrid does little more than turn on the computers.

NemesisUK · November 13, 2018

42 minutes ago, Northern_Si said:

My understanding is that the 12v battery on the hybrid does little more than turn on the computers.

Plus power the easy entry and alarm systems?

IIRC the entry system shuts down after a prolonged period of inactivity.

So, yes the 12v Battery doesn't have any great demands on it..

Britprius · November 15, 2018

While I agree at first sight on the hybrids there does not seem to be a great advantage in fitting a larger capacity Battery. In fact there are are number of advantages.

The ability to be able to sit in the car listening to music or even watching a DVD without having to have the engine start up on a regular basis.
The car can stand much longer periods of non use without the Battery getting to the point where it cannot boot to ready.
As a battery ages it looses capacity. Using a higher capacity Battery helps reduce this effect. Loosing 50% of the 70 ah OEM Battery capacity means the actual capacity would be 35 ah. Loosing 50% of a 110 ah Battery means it would still have 55 ah's capacity left important as the Battery ages.
The difference in price is negligible if any at all.

With non hybrids where a normal stater motor is used the higher capacity makes a big difference to engine cranking particularly in the cold.

Be cause of space restrictions the CT only has a 45 ah Battery, but still has much the same demands put on it as other hybrids such as the Prius. Having owned a Prius, and from reports in the CT section I know the Battery in these vehicles is inadequate for it's purpose. Many reporting the inability to go to ready mode after standing at at airports ect, and having to resort to using external chargers at home to help bolster the Battery capacity.

John.

Farqui · November 27, 2018

Is that replacement an AGM Battery John?

Britprius · November 29, 2018

On 11/27/2018 at 5:36 PM, Farqui said:

Is that replacement an AGM battery John?

The Battery I used was not an AGM. The particular Battery was a sealed deep cycle marine leisure Battery although it would be reasonable to fit any lead acid chemistry Battery. There are AGM batteries sale on eBay, but they tend to be more expensive. I did notice a BMW, Range Rover start stop AGM at 85 AH priced at £65 for a 1 year guarantee or £97.50 for 5 year guarantee. These are slightly shorter batteries than the Battery I fitted at 310 mm against 330 mm, but would still need the tray modifications.

If you wish to use an AGM Battery I would use a "mobility" Battery of 110/120 AH capacity

There is no reason to use an AGM Battery in the GS range since the Battery is in the boot, and there is no chance that in an accident car occupants are going to get covered in acid. The OEM Battery does not appear to be an AGM, and had no markings to show that it was.

In the case of the Lexus CT200h, and the Prius where the Battery is in the passenger compartment "although well covered" it is perhaps desirable to have an AGM Battery with no free liquid acid to spill.

Using a higher capacity Battery means that any given number of AH's discharged against the 70 AH OEM Battery the % discharge figure "depth of discharge" will be lower. The shallower the discharge cycle the longer the life of the Battery.

John.

Farqui · February 4, 2019

John @Britprius, I've been considering replacing my 12v Battery as it's a Panasonic unit so could well be original ! But I wondered how fitting a larger Ah unit would affect the hybrid electronics? You've done this and I'd like your feedback on how it's panning out.

The OEM Battery is rated at a measly 45Ah (which is fine as it isn't used to crank the combustion engine) and the hybrid electronics are responsible for keeping this topped off. Charging the traction and 12v boot strap Battery is via the combustion engine and via regen to a lesser extent.

So if you fit a larger Ah boot strap Battery then will the hybrid electronic's trigger a longer combustion cycle to charge it and thereby rob you of mpg's?

I recall someone mentioning recently that they found the combustion engine was firing up for longer with a tired, old 12 boot strap Battery. Replacing the Battery apparently gave them better mpg's, which could well be down to a subsequent reduced combustion cycle right? Or might the boot strap Battery disconnect during replacement have reset the vehicles computers and loaded an improved base setting rather than a time learnt setting?

The hybrid electronics are fiendishly clever and I wonder if the system is rated and built to be as efficient as possible for that vehicle.

I guess I ought to test my 12v boot strap Battery and figure out how it's fairing...

Farqui · February 4, 2019

Maybe I'm overthinking it as all the batteries are 12v

Herbie · February 4, 2019

1 hour ago, Farqui said:

Maybe I'm overthinking it as all the batteries are 12v

Yep, you are Lee.

12V is 12V is 12V and the type of Battery chemistry or Ah rating won't affect the hybrid side at all, or at least not in the context that you're thinking. A brand new Battery should be fully charged or not far off, so it shouldn't take much to bring it up to full and keep it that way.

The combustion engine will still fire up to keep it charged up as and when it needs to, but it won't be any more or any less frequent just because you put a larger capacity Battery in the car. There will be a lower voltage threshold that will trigger the engine to come on and a higher voltage threshold when the engine will turn off and those values won't change depending on the capacity of the 12V Battery.

ColinBarber · February 4, 2019

2 hours ago, Farqui said:

So if you fit a larger Ah boot strap battery then will the hybrid electronic's trigger a longer combustion cycle to charge it and thereby rob you of mpg's?

The 12v Battery is charged by the hybrid system, not the ICE, but obviously if the hybrid Battery gets low the ICE will start up.

Having a bigger Battery in itself won't mean it needs greater charging - only if you use that extra capacity, and in the times you need that extra capacity (e.g. three weeks on holiday) I'm sure a little, almost undetectable, drop in mpg is way less of an inconvenience than not being able to start your vehicle.

Britprius · February 4, 2019

3 hours ago, Farqui said:

John @Britprius, I've been considering replacing my 12v battery as it's a Panasonic unit so could well be original ! But I wondered how fitting a larger Ah unit would affect the hybrid electronics? You've done this and I'd like your feedback on how it's panning out.

The OEM battery is rated at a measly 45Ah (which is fine as it isn't used to crank the combustion engine) and the hybrid electronics are responsible for keeping this topped off. Charging the traction and 12v boot strap battery is via the combustion engine and via regen to a lesser extent.

So if you fit a larger Ah boot strap battery then will the hybrid electronic's trigger a longer combustion cycle to charge it and thereby rob you of mpg's?

I recall someone mentioning recently that they found the combustion engine was firing up for longer with a tired, old 12 boot strap battery. Replacing the battery apparently gave them better mpg's, which could well be down to a subsequent reduced combustion cycle right? Or might the boot strap battery disconnect during replacement have reset the vehicles computers and loaded an improved base setting rather than a time learnt setting?

The hybrid electronics are fiendishly clever and I wonder if the system is rated and built to be as efficient as possible for that vehicle.

I guess I ought to test my 12v boot strap battery and figure out how it's fairing...

Lee I think others have answered for me, but the charging system is well capable of charging a higher capacity Battery. It has a maximum output in excess of 100 amps, but it is also Battery temperature controlled. The reason for the small sensor with two thin wires that can be gently eased out of the OEM Battery and fastened to the top of the new Battery with tape, glue, hot melt glue, or even blue tack.
I have had no problems with my 110 AH set up. I do have the piece of mind knowing that if I sit in the car for two or three hours with the radio on or watching a DVD or even leaving the car for a month or more it is going to boot up when needed.

John.

Farqui · February 4, 2019

Good news then.

I almost dare not say it but the OEM Battery always starts mine after a week or two sat on the drive. Hopefully I've not jinxed it now!

I'm still curious why a new 12v Battery can help improve mpg?

acepower84 · April 11, 2019

Sorry to open this topic up again but if i wanted to get an OEM spec Battery, what would i be asking for at motorfactors? I did get one listed for the car but it is too big and it has also caused the error VGRS to pop up.