Solution for weak 12v battery which occurs in most hybrid vehicles and LC250 ?

[t3lcfe]

Many many of us had bad experiences with our LC 12v battery. If you just leave the doors opened for not too long for unloading stuffs or working on something on it, the 12v battery drained and vehicle cannot start !!!

Some folks here changed the oem battery with super duty AGM battery, but the hybrid system will not top off and maintain with full charged (mostly just hanging at around 60% of AGM capacity) so what is the point ?
Some of us here had to add permanently solar panels on rooftop (under roof rack) to keep battery at stable state !
I love and love EVERYTHING about my FE, except battery “shit” ! I always carry TWO super duty jumb starters and 2000w Jackery (mainly for my fridge, but also last solution for the damn oem battery !)

Last week, we family of 4 took FE to overland and camping in primitive/ off-grid areas. As all the times, we go by ourself with no other rigs. At least 3 times, my wife and kids opened the doors /hatchback to get foods and stuffs … just few short minutes…and guess what! Engine couldn’t start. Freaking scare that happened in no where in woods. Luckily, I had 3 “backup” things mentioned above which helped me to start the engine. It’s damn inconvenient and frustrated. Since that 3 times happened with weak battery, I had to run the engine before / during opening the doors to access stuffs in the trunk.

Now, I found couple solutions here which maybe helpful:
1/ battery monitor/ alarm: let us know real-time the status / current of its charging…and alarm us when it is going to die. However, it just help a bit : Ancel BM300 or BM200 Pro Battery Monitor
2/ super starter / permanent mounted/connected to 12v battery: always there and top off capacity and guarantee to supply 700A start assist just in case the 12v battery is weak or died

I will test these products at home garage with opening all the LC doors. I am leaning more about solution 2/
Again, ultimate LOVE to my FE so I must figure out how to live with its “small battery” ! I can live with small fuel tank by carry few more Rotopax spare fuels


Note: I have never had that terrible/freaking scare experience with weak battery like that with my Gwagon for 8 years till now….Come on LC250 !

 

[basicxj]

Staying tuned.

I am leaning towards installing a "super-duper" AGM and getting into a routine of topping it off with a charger as needed. I would prefer to have a little more redundancy than provided off the showroom floor. I have a Noco jump pack I keep handy in the vehicle and a spare at home. I also have a peek at the state of charge of the battery by plugging in an OBDII dongle and checking with Carista periodically.

 

[wpage]

Anyone know the limit of size dimension for the battery compartment? Would a oversized battery help with the stated failure conditions^^^.
It is good to keep a battery booster for when failure to start occurs. Many are not ready to install solar remedies to this problem which seems common... So whats the cure here??

 

[phxdsrtrat]

I've run a 12 volt fridge off my 12 volt battery in my LC for a couple of days without an issues. I find it hard to believe a few LED lights would drain the battery to a level that would not allow the vehicle to start. The 12 volt charging system definitely charges the battery to above 60% also, verified with a volt meter showing 12.76 volts. If it were at 60% I would expect to see somewhere around 12.35 to 12.40 volts. Since AGM is still lead acid chemistry there is no difference in its charging profile. Going LiFEPO4 would be an option to get more energy out of the battery which would be good for overlanding. However, most LiFEPO4 batteries do not make good starter batteries. There are a few exception out there specifically built for vehicle applications with a built in BMS that handles the charging profile without modifications to the vehicle.

The products mentioned in this thread are good insurance. I have jumper packs in all my vehicles. However, I do believe the original poster may have more of an issue than just a small battery. Maybe some other parastic drain, bad charging system, etc. Definitely worth looking into before replacing the battery.

Someone asked about the battery size. From what I've seen a larger physical form factor battery is probably not possible. The battery is a Group 48 (H6} battery.

My battery is getting long in the tooth for the Arizona heat at 2 years. You usually don't get much over 3 years out of a battery in our weather conditions. I'm thinking of going sodium ion for my next battery. They don't have any more capacity than a standard lead acid but they can be drained lower than 50% without damage which is not the case with lead acid. Here is the short list of batteries I'm considering for reference..,.,

Sodium Ion
LiFEPO4
AGM

Each chemistry has its own advantages and disadvantages. I would avoid the high capacity RV type batteries as they don't make good starter batteries.

-Curtiss

 

[EOD Guy]

Anyone know the limit of size dimension for the battery compartment? Would a oversized battery help with the stated failure conditions^^^.
It is good to keep a battery booster for when failure to start occurs. Many are not ready to install solar remedies to this problem which seems common... So whats the cure here??

The 12v battery hold down limits the battery size. If you were to modify the hold down, you might be able to get a slightly larger size in there, but there's not a lot of room in that space.

 

[D-mac]

There's drop in Group 48 lithium batteries if you don't think AGMs are quite good enough. The sports car/track racing crowd uses them, but they're just starting to enter the 4x4 "overland" market. . The more expensive batteries have some cool built in remote/app monitoring and self starting capabilities.
I think someone on here made the modifications to put in a larger Group 27 AGM battery too.

 

[Area 51]

Mine is not weak or has been unreliable in any way at 18 months and 16k miles.
A peak charge every 6 moths helps and will prolong the life.
Garaged, mild nor cal weather that helps too.

 

[t3lcfe]

Mine is not weak or has been unreliable in any way at 18 months and 16k miles.
A peak charge every 6 moths helps and will prolong the life.
Garaged, mild nor cal weather that helps too.

I will check with dealer if it is still under manufacture warranty and probably it can be replaced for “free”
Anyway, I hope the 2 methods I mentioned will bring a huge peace of mind while in remote/ overland

 

[Mopper]

I'm with @Area 51 , haven't seen a hint of any issue 6 months and 13.5k miles in. That said, I'm heading out for the first real overlanding trip in this vehicle soon. Talk of dead batteries spooked me and I ordered a smaller NOCO Boost (GB20) last week. Perhaps somewhat helping, I previously installed @EOD Guy 's Lift Gate LED Switch (and it's almost always in the off position)

 

[t3lcfe]

I'm with @Area 51 , haven't seen a hint of any issue 6 months and 13.5k miles in. That said, I'm heading out for the first real overlanding trip in this vehicle soon. Talk of dead batteries spooked me and I ordered a smaller NOCO Boost (GB20) last week. Perhaps somewhat helping, I previously installed @EOD Guy 's Lift Gate LED Switch (and it's almost always in the off position)

Instead of installing the switch like yours and EODGuys, most of time if I don’t need hatchback light and all interior ones, I just use a stick, key, or screwdriver to kick the latch so all is off
However, in remote and overland at night, we do need lights in trunk to get stuffs in and out.
BIG lesson learned, just turn on engine before and during your “operation” in the trunk with opening and Lighting up. It is not RIGHT, but my temporary solution … I will try the BS200 ( hopefully it is not BS

 

[ultane]

Since AGM is still lead acid chemistry there is no difference in its charging profile.

Are you sure about that?

 

[ultane]

I will check with dealer if it is still under manufacture warranty and probably it can be replaced for “free”
Anyway, I hope the 2 methods I mentioned will bring a huge peace of mind while in remote/ overland

I would ask them to ‘load test’ your battery.

 

[Mopper]

Instead of installing the switch like yours and EODGuys, most of time if I don’t need hatchback light and all interior ones, I just use a stick, key, or screwdriver to kick the latch so all is off
However, in remote and overland at night, we do need lights in trunk to get stuffs in and out.
BIG lesson learned, just turn on engine before and during your “operation” in the trunk with opening and Lighting up. It is not RIGHT, but my temporary solution … I will try the BS200 ( hopefully it is not BS

Just checked out your solution- great. I may wind up experiencing the buy twice, cry twice phenomenon. We'll see. Here's a link-
BS2000

Still hoping my LC is different! (And thanks for both tips- rigging the latch and firing up for use)

Edit 9/25/26: completed a 10 day 1500 mile camping trip and have gone through the past 3 months without any battery issues. Seriously wondering about not so good OEM lead/acid batteries and @GR8Santini 's observations here -> Quote. I think it might be a combination?

 

[phxdsrtrat]

Are you sure about that?

What I should have said is you don't typically need to do anything to your charging system in most vehicles to drop in an AGM. They technically do have different charging profiles.

-Curtiss

 

[t3lcfe]

Just checked out your solution- great. I may wind up experiencing the buy twice, cry twice phenomenon. We'll see. Here's a link-
BS2000

Still hoping my LC is different! (And thanks for both tips- rigging the latch and firing up for use)

Man…I did quick research and found that “battery weak” problems happened within TOYOTA hybrid vehicles … it is “common” (?)
In YouTube, there are many explanation videos.

One thing I forgot to mention (just remembered) that full time I had to use rear camera in rear mirror ( guess only equipped in higher tier/trim LC) because of my carry stuffs filled up/blocked entire rear window so couldn’t see anything without rear camera. When stopped at remote campsite, I still left it on…it could suck some juice from small/weak battery as well !
Here are couple videos I watched from YouTube. For sure, there are more depth and engineering explanations out there…

 

[phxdsrtrat]

There is an existing theead with some great info...

Observations and speculation of 12v-battery charging system

A couple months after buying my 2025 LC (base, premium), I spent a few days installing cargo drawers. The 12v battery died because I ignored the warnings in the owner's manual and kept the rear hatch open for many hours (without using the carabiner trick). Since then I've been following the...

www.landcruiserforum.com

 

[wpage]

The 12v battery hold down limits the battery size. If you were to modify the hold down, you might be able to get a slightly larger size in there, but there's not a lot of room in that space.

Thanks EOD ^^^ When my warrentee is up going to try a mod and jam something bigger. I like Marine type batties with the wing nut taps on top for options.

 

[Markarian421]

Man…I did quick research and found that “battery weak” problems happened within TOYOTA hybrid vehicles … it is “common” (?)

Yeah my brother’s Prius keeps killing his 12v battery too.

 

[t3lcfe]

Yeah my brother’s Prius keeps killing his 12v battery too.

Is it right ?! Many things make sense to me …

 

[Mopper]

Is it right ?! Many things make sense to me …

Seems kinda sensationalist to me. Notice that even though 'published' recently, most of the hard dates mentioned are earlier 2020s and that Big Bad Corporate Keep Secrets Toyota is alluded to for an undisclosed plot to hurt their customers a couple times. That and some of the AI-revealing pronunciations ("eye-em-balance", for instance) make me skeptical. But I always am a skeptic. I think the other thread that @phxdsrtrat pointed to is a good resource. I'm either lucking out with my 10-15 minute typical drive, getting in enough longer drives around the shorter one to mask the issue, or really am playing with fire (incoming NOCO Booster). I intend to establish a way to evaluate 12V charge readiness.

Engineering wisdom: if you can't measure it, you can't control it. If you don't control the critical variables, you're just a victim waiting for the 'accident'.