AGM + Lithium Dual Battery Setup Options

[adair0 Lurker Find all posts View Profile Close adair0]

I'm just after some advice from seasoned veterens when it comes to dual battery setup and fit-for-purpose options.

Prado 2016 150 series GXL.

Current Setup is starter battery + AGM Deep Cycle (All Rounder) 105ah with Projecta dc/dc (non lithium compatible) charger. Anderson plug on air filter presumably for Solar. Anderson plug on the rear tow bar too. 12v sockets with voltage display in boot of car.
Both batteries need replacing according to supercheap battery tests though. I have a winch connected to cranking battery also.

Options I could see are below but very open to feedback.
I'm adding $200 to each option for solar panels.

Option 1: Replace AGM & cranking like for like $650
Pros: Cheapest option, Car is already setup for it so no tinkering needed.
Cons: Only has 50% usable amp hours. Outdaded battery technology. Lifecycle much shorter. Am limited to using 12v in car. Have to take fridge with me if doing day trips. About 50kg more compared to other options = much more fuel over lifespan of product.

Option 2:
Dual Lithium 120AH batteries + Lithium compatible dcdc charger $1500
Pros: 2000 charge cycles each at least. Will last life of the car. 50+kg lighter = fuel savings over lifespan. Redundancy. Wouldn't have to rewire everything outside of the dcdc charger.
Cons: Still limited to using 12v in car sockets. Have to take fridge with me if doing day trips.

Option 3:
Replace AGM Deep Cycle 138ah + buy lithium 120ah with battery box $900
Pros: have redundancy. Ability to leave fridge at campsite for day trips. Don't have to rewire anything. Can connect solar to either battery setup. Not required to park vehicle next to camping spot
Cons: I don't think I can charge the lithium through the cars Anderson plugs if my i leave dcdc charger as is (non lithium compatible)?

I'm a noob when it comes to this stuff so appreciate all the advice or new options I haven't thought of yet.

Thanks,
Adair

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

If your going to replace the cranker with a Lithium then it will ahve to be directly charged off the alternator. If your going to do that then you may as well directly charge the Aux Lithium using a simple VSR setup. You will need batteries that can handle direct cherging off an alternator like the DCS ones.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

Hi Adair0,

The article in this link is not a bad guide to understand battery tech for 4x4s 4x4 batteries buyers' guide - CLUB 4X4

You have two different applications to deal with:

• Cranking and winching
• Powering accessories/trailer

For Cranking and winching you will most likely struggle to find a Deep Cycle AGM or Lithium that is rated for under bonnet use and capable of either of these tasks (particularly sustained winching). So I would recommend getting the highest AH rated good quality dual purpose starter style battery that fits in the cradle. Dual Purpose batteries are starter batteries that are also capable of supplying sustained low to moderate current draw from accessories without reducing service life but do not have the same depth of discharge or cycle life as deep cycle batteries in that role. Examples of these are the Optima Yellow top, Century Dual Force, various marine dual use batteries.

For powering accessories and trailers you are generally supplying low to moderate loads over sustained periods so you do want a deep cycle, so you can use either a dual purpose, deep cycle or lithium but what you select is also affected by installation location as if under bonnet be careful if you choose lithium that you get an under bonnet rated and warranted version.

On the DC/DC charger front, most good quality 12V lithium batteries have a BMS that will cope with most standard chargers so I wouldn't bother changing your Projecta DC/DC over until it fails or you want to upgrade for other reasons. The closest setting to lithium profile on the Projecta is AGM with 14.4v charger profile just don't use Calcium as the lithium won't like the equalisation cycle that it does in that mode .

In my old Hilux I had an Exide Extreme for Cranking/Winching, ITechworld 120 Lithium as Aux in rear tub and another ITechworld 120 Lithium in a battery box to use as needed.

In my current Prado I am using the OEM battery for cranking winching until it gives me trouble and will upgrade to Optima or Century Dual Force at that time, slimline 100Ah Lithium between rear seat and fridge box for vehicle accessories, plus still have the Itechworld 120 battery box for when needed.

Sorry a bit long winded but hope this helps

Cheers Phil

[adair0 Lurker Find all posts View Profile Close adair0]

Thanks Phil this is exactly the sort of insight I was after.

Thats great about the dcdc charger as it saves me $300 straight away and gives me the option for a lithium.
So with the information you provided, getting a dual purpose battery as the main is required regardless, to support the winch. (though I looked at a few videos and they claim lithium works fine for winching as long as the car is running?)

Given I can use the existing dcdc configured to AGM setting for lithium, now my thoughts are to have 120ah lithium as auxillary battery (means it gets charged whilst driving), and also buy a battery box for when I need to do day trips I just disconnect the lithium and leave it behind with the fridge. Would disconnecting this lithium auxillery battery have any negative affect on the main dual purpose battery or setup if the thw wiring is sitting there disconnected? Basically I am just trying not to break the bank and buy 3 batteries right now.

Again, thanks for the great info and links, it's all coming a bit clearer for me now.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

Hi Adair0,

Even though it is normal to winch with car running to reduce the battery current draw, there are situations where being able to winch without it running may be needed/beneficial. I'm not convinced yet of the long term reliability of under bonnet lithium's used in starting/winching roles and in my opinion cost vs benefit is not quite there yet.

You should be able to disconnect your aux battery (Lithium or otherwise) from the Projecta DC/DC and it should shut down the charge functions as it senses the battery is connected before starting up. I would still ensure the aux battery leads are secured and insulated when not in use.