2018 LX570 Dual Battery System w/ AGMs - AGM starting/main battery

[WanderOver]

Has anyone managed to find a solution for running dual AGM batteries on the newest 200 series and LX570s that do not have a fuse in the ALT-S location? Obviously the Redarc system would work for keeping the second battery charged but what about the main/starting battery? With the smart alternator, it does not like to keep the main battery topped off due to the AGM charging profile. Has anyone made this work? Or is the only option to go back to Flooded Cell factory battery for starting with AGM/Redarc house battery? Any ideas greatly appreciated.

P.S. this is for @Chrisleduc1's LX570. Slee sliders going on this week!

 

[OregonLC]

What is your (his) goal for having the AGM for the starting battery? If you've already installed an AGM it will work just fine as a starting battery even though it won't be in an ideal state of charge. I ran a group 31 in my 100 for years with no problem. I wouldn't change back to flooded at this point. Though, if Toyota still supplies Panasonics that OE batt is a very good battery and would certainly be worth keeping. I also wouldn't mess tampering with the OE charging bits on a new truck still under warranty. I would let them run as two separate systems with the BCDC keeping the house battery in shape.

OTOH, if you're hoping to use it as a deep cycle to augment the second battery then you'll need to find a different charging solution.

 

[WanderOver]

What is your (his) goal for having the AGM for the starting battery? If you've already installed an AGM it will work just fine as a starting battery even though it won't be in an ideal state of charge. I ran a group 31 in my 100 for years with no problem. I wouldn't change back to flooded at this point. Though, if Toyota still supplies Panasonics that OE batt is a very good battery and would certainly be worth keeping. I also wouldn't mess tampering with the OE charging bits on a new truck still under warranty. I would let them run as two separate systems with the BCDC keeping the house battery in shape.

OTOH, if you're hoping to use it as a deep cycle to augment the second battery then you'll need to find a different charging solution.

Have already changed over to dual odyssey AGMs. Currently running Blue Sea ACR system, looking at adding BCDC for house battery. Starting Odyssey has less than one year of usage and resting voltage is 12.2-12.3 after being charged via external battery charger. Leads me to believe the factory charging system is just not keeping it healthy. Would prefer to stick with both AGMs, however need to find a long term solution other than charging starting battery externally regularly or replacing once a year. Have run same setup in other rigs with success, utilizing voltage booster as needed in certain applications that have ALT-S fuse in place. Trying to make it work in this one.

 

[TeCKis300]

It's a tough problem without any direct solution. The stock alternator/regulator has a charge profile tailored to flooded lead acid. Short of changing that, it's going to dictate an FLA battery.

It would be like a BCDC with mode switch stuck in FLA charging profile. Then forcing an AGM battery to charge on that FLA profile. Not ideal.

There are alternators out there, including OEM alternators with regulators setup for AGM. It would take some discovery to see if anything is adaptable to the 200-series.

Compounding this that AGM batteries don't like heat to begin with and are not as resilient to underhood temps. An optimal charger will have temperature charging compensation, that tapers voltage with increase heat, so as not to boil out the electrolytes in an AGM battery. Yet that greatly compromises charge rates. Diodes don't work, because what that does is elevate the voltages that can already cause an AGM to vent when charging in high temps, further exacerbating the situation.

There's no point to an AGM battery as a starter battery when they're going to only last 2-3 years. Been there done that. Nothing wrong with an FLA batt that lasts 5-7 years as the manufacturer intended.

IMO, a high quality, perhaps larger group size FLA in the starter position is the optimal solution.