The 12-volt auxiliary battery is a quietly essential component of your vehicle’s electrical architecture. It provides the primary source of power for all low-voltage systems, including lighting, climate control, audio features and, where fitted, the starter motor. While modern vehicles incorporate significantly more technology than those of previous generations, the fundamental principle remains unchanged: the 12V battery is replenished through the operation of the powertrain.
This cycle of energy consumption and replenishment has underpinned automotive engineering for over a century. Renowned for its reliability, it is largely self-sustaining. Nevertheless, an understanding of the system and a few considered practices can help ensure the continued health and longevity of your vehicle’s 12V battery.
Common causes of 12V battery concerns
Most issues arise when the battery is not given sufficient opportunity to fully recharge. It takes a little time to reinstate the charge that was expended from the battery at start-up – longer if multiple electrical systems are operating simultaneously. Frequent short journeys can therefore gradually reduce the battery’s charge.
Low ambient temperatures also place additional demands on the battery. Cold conditions slow the internal chemical processes, making start-up more demanding and accelerating charge loss. At the same time, increased use of heating, ventilation and lighting further draws on the battery’s reserves.
Recommendations for preserving battery health
1) Regular operation
Where possible, aim to take your car on a 30-minute journey at least once a week. If this is impractical, or if the vehicle will remain unused for an extended period, a high-quality battery maintainer (also known as a trickle charger) is recommended to sustain optimal charge levels. Your local Lexus Centre can advise whether a mains-powered or solar solution is best suited to your needs.
2) Consolidate journeys
Repeated short trips can prevent the battery from fully recharging. Combining errands into a single journey helps mitigate this effect. Brief stops during a longer trip are unlikely to be detrimental, as a warm engine and cabin require less energy to restart and maintain.
3) Minimise unnecessary electrical load
When the powertrain is not operating, the battery is not being recharged and therefore electrical features such as lighting, ventilation and audio systems will continue to draw power. To preserve charge, ensure these systems are switched off before turning off the powertrain. This also reduces the load placed on the 12V battery during the next start-up.
4) Monitor battery condition
Periodically inspect the battery terminals for signs of corrosion and ensure all connections are secure and clean. These checks form part of your vehicle’s scheduled service programme at your local Lexus Centre, but the team there will also be pleased to provide guidance at any time.
12V batteries in electrified vehicles
Hybrid and fully electric vehicles are equipped with two batteries: a 12V auxiliary battery that supports low-voltage electrical systems, and a high-capacity traction battery that powers the electric motor(s).
In both cases, the 12V battery is only charged when the vehicle is in READY mode. For this reason, we recommend keeping the vehicle in READY mode whenever you remain in the vehicle while using electrical features – for example, when listening to the audio system while waiting.
If assistance is required
By following the guidance above, issues with the 12V battery are unlikely. Should a concern arise, however, reassurance is close at hand – expert assistance is always just a phone call away.
Breakdown cover arranged through Lexus Roadside Assistance offers year-round support, 24 hours a day. Delivered in partnership with The AA, the UK’s number one provider, this breakdown cover includes jump starts, towing and emergency roadside assistance. In addition, the nationwide network of Lexus Centres is also available for advice or assistance.
FAQs:
How can I make sure the 12V battery is in good condition after it has been parked for an extended period of time?
Consider using a quality battery maintainer to keep the charge level topped up. Lexus Centre staff will be able to advise on whether a mains- or solar-powered option is the best for your circumstances.
How do I put my vehicle in READY mode?
READY mode only applies to full hybrid or full electric vehicles. First, ensure the transmission is in PARK and that the handbrake or e-brake is engaged. Then apply the foot brake and press the vehicle’s START button. Green READY lettering (see image below) will illuminate on the dashboard to confirm that this mode is now active.
NB: Remember that if the powertrain is not active, low-voltage accessories like the lights, ventilation and audio system will all draw power from the 12V battery.
Will using a dash cam affect the 12V battery?
Lexus approved accessory dash cams should not cause any drain on the 12V battery when the vehicle is switched off and parked. However, when the dash cam is active, ensure the powertrain is either running or the vehicle is in READY (not ACCESSORY) mode to prevent draining the 12V battery.
Does using connected services on the Lexus Link+ app drain the 12V battery’s power?
Yes, a very small amount of power is drawn from the 12V battery when owners use Lexus connected services. Refreshing the vehicle status in the Lexus Link+ app can wake the vehicle, so make sure to follow our battery maintenance recommendations if you regularly refresh your vehicle’s status.
What should I do if I’ve received a ‘Starter Battery Low Charge’ alert from the Lexus Link+ app?
The Lexus Link+ app does not directly monitor the charge level in the 12V battery (starter battery) but is programmed to predict its health and alert owners as a result of other factors, such as the infrequency of the vehicle’s use. The alert is therefore a calculated suggestion that the battery would benefit from the vehicle being driven for at least 30 minutes.
NB: Notifications can take 24 hours to clear from the app after the vehicle has been driven.
Is the 12V battery covered by the Lexus manufacturer warranty?
Yes, the 12V battery is covered by our manufacturer warranty for up to three years or 60,000 miles, whichever comes first. This includes any failure caused by defects in manufacturing or assembly.
I have been seriously considering replacing my 2011 RX350 with a 450h plus! I have read a ton of forums complaining about this 12 volt charging system. I’m definitely rethinking my purchase. This would be my 4th Lexus, always so impressed with their quality. Looking at the price of the 450h plus this problem is inconceivable! Why should you have to purchase a trickle charger and a booster after spending this much money on a car? The Toyota Rav 4 Prime has a system that also charges the 12 v battery when it’s plugged in. Why can’t Toyota do that with the Lexus Hybrids?
When checking my 12v battery state of charge before and after a purely EV run of 40 miles, I note that the battery charge had only increased by 1 or 2%. (From 50%)
Has the Lexus system been set up to put as much as possible of the high voltage EV battery into mileage and token charge into the 12v battery?
After experiencing several flat batteries, I assumed that my 4 year old 12v battery was to fault and replaced it but now I’m not so sure.
Morning Kevin, thank you for getting in touch.
Please may we take your car’s registration?
Thank you.
Whatever you do, don’t buy the RX 450h.
I bought my first Lexus after 35 years of buying prestige cars with generally no issues.
I went for the RX 450h Takumi after being sold on its perceived high reliability and experienced a battery failure last week. This is a first after many years of successful car ownership across other brands. The whole episode ended up being a nightmare, with the key reason being given that I don’t drive the car enough. So in essence, my fault. The car has done 7000 miles within its first year and does regular long journeys.
The car is booked in next week with Lexus Edinburgh for an inspection and I’m intrigued to see what is said and offered.
What is now very clear and I wish I had known before is that Lexus have a significant problem with the 12v battery set up. Reading the range of comments posted, this has put many people in a range of difficult and unacceptable situations.
Good afternoon Walter,
Sorry to hear you’ve recently experienced a problem with your Lexus RX.
We’re pleased you’ve made arrangements to visit your local Lexus Centre and trust that they will look after you and your car going forward.
Thank you.
I have just driven from my home to Bath and back, a distance of 44 miles , and received an email saying the 12V battery was at a low charge. My LBX is only 18 months old and I was assured this would not be a problem. Surely Lexus have a solution to this problem? They cannot expect owners to accept this obvious design fault.
If there is no solution I will consider selling the car.
Good morning Roger,
We’re sorry to hear you’ve experienced problems with your LBX 12V battery.
Please get in touch with your local Lexus Centre to arrange a free 12v battery inspection if you are still having troubles.
Additional advice can be found here: https://mag.lexus.co.uk/lexus-wont-unlock/
Kind regards.
Purchased Lexus RZ 300e from new just over a year ago (My 3rd Lexus (IS/NX), last year had several instances of dead battery, took to Lexus Belfast who eventually replaced the 12v battery as good will. Fast forward to 2027, same issue has occurred again 3 times in 5 weeks, luckily I had bought a battery booster to save embarrassment of boosting a Lexus from a Forklift at work. I now regularly trickle charge for some modicum of reliability. All three cases this year have occurred when unhooking from 11kw charger and yes I regularly do 30min plus journeys and much longer (11-12k per annum). Does Lexus recognise this issue and is there a service bulletin or software update to resolve? I am assuming that when charging the 12v is not charged. My wife now refuses to drive this vehicle and I use a spare car (Fiesta) when leaving at airport for work. This has seriously tainted my view of Toyota/Lexus reliability after having owned both brands. I am not alone judging by the number of comments on both this magazine and multiple Lexus forums.
Good morning Joseph,
We’re sorry to hear you’ve been experiencing these problems with your Lexus RZ.
We’d kindly ask that you get in touch with your local Lexus Centre to arrange an inspection so they can advise further.
Thank you.
I received a message via the app telling me my Lexus LBX battery was running low! As we were about to go away for a week we put it in the garage on trickle charge. One week later we returned home to receive another message saying that my battery has run low and this is without being used and whilst connected to an advised charger! I won’t be getting another Lexus!
Good morning Val,
We’re sorry to hear you’ve experienced ongoing problems with your 12V battery.
Please get in touch with your local Lexus Centre to arrange a free 12v battery inspection if you are still having troubles.
Additional advice can be found here: https://mag.lexus.co.uk/lexus-wont-unlock/
Thank you.
At last confirmation that I’ve not lost the plot! Today we have had a flat battery for the 4th time on NX 450+h. Having had the car on charge overnight it was unlocked and tailgate opened for our dog this morning. On closing the tailgate we went to enter the car only to find zilch. This is so infuriating as there seems to be no logical explanation. We were fortunate that at least we were at home and not stranded in an isolated car park this time. When the AA arrived it was a simple start again and the battery health check proved to be fine. Nevertheless, had we known of these issues when we bought the car in 2024 we would have been out of the showroom in a blur.
As this is our first Lexus it is also likely to be our last due to this ridiculous issue. It It is the last thing we would expect from “luxury “ manufacturer as portrayed by Lexus
Good morning Viv,
We apologise that you are experiencing issues with your 12V battery.
We would recommend visiting your local Lexus Centre for a 12V battery inspection.
Additionally, please read our article for any additional advice: https://mag.lexus.co.uk/lexus-wont-unlock/
Kind regards.