I have been scratching my head and doing some research about this topic. My AAA Branded AGM (H8) battery (date coded to 09/2021) died suddenly and spectacularly on Sunday almost leaving us stranded. Luckily I had a NOCO jump starter with me and managed to get it home. Had to clear trouble codes a couple times with the GAP tool because of insufficient voltage that kept putting the car into limp mode - no power and refused to do more than 10mph. AAA won't honor the warrantee on the battery, so I will be buying a new battery.

Since the car is 17 years old with 127K miles, I thought it may be a good idea to just renew the alternator, drive belt and tensioner pulley at the same time. Got some prices for a new OEM Denso alternator (Cheapest I could find was for $250) and looked at the specs (Peak 150A and 90A produced at Idle). Since I want to install a winch (500A), DC to DC charger (50A) and some driving lights and seeing that the LR3 is so sensitive to undervoltage situations, I started looking at high output alternators.

I had a look at and spoke to the following high output alternator companies:
1. Quality Power - Based in CA - 140A idle, 240A Peak - Voltage regulated at 14V - Price $425 - Lead time = 5 days to build.
2. Power Bastards - Based in CA - 125A idle, 250A Peak - Voltage regulated at 14V - Price $425 - Lead time = Same day dispatch.
3. JS Alternators - Family business based in SC - 180A idle, 250A Peak - Voltage Regulated @ 14V/14.8V (you can specify) - Recommends 0.5" Smaller serpentine belt, and big 3 cable upgrade - Price $359 - Lead time = 15 days to build.
4. Tucson Alternators - Family business, based in AZ - 190A idle, 250A Peak - Voltage regulated @ 14.8V - Recommends 0.5" shorter serpentine belt, and big 3 power cable upgrade - Price $379 Lead time = 24 to 48h.

Two of these companies advise on their website - and also did so on the phone - that every high output alternator should be accompanied with a big 3 power cable upgrade. This makes sense, as there is no point in installing an alternator capable of delivering almost double the amperage if the power cables cant cope. The way of doing so is installing the new cables in conjunction with the standard cables (essentially in parallel).

I also read a lot about AGM Batteries and the voltages required to charge them. I even called Full River in California on advise from JS Alternators. For bulk charging, AGM requires 14.3V at 104F and 15.3V at 32F. Float charging requires 13.4V at 104F and 14.3V at 32F. We know that our OEM alternators will not deliver those voltages, so our alternators fail to ever recharge AGM batteries fully, which "significantly shortens their lifespan" (I have read this multiple times).

Questions:
1. If I consider that most of the battery manufacturers give a 3 year warranty on batteries, and my AGM battery lasted 35 months, I can only deduce that AGM expected lifecycle is roughly 36months. How much more could I expect if the AGM battery is charged exactly right? How does that compare to a Lead Acid?
2. If I were to install an alternator with a 14.8V regulator, I wont ever see 14.8V because the alternator output voltage is controlled by the vehicles ECU. So I can never fully charge an AGM battery?

Conclusion:
There is no benefit to installing a high output alternator in combination with a flooded lead acid battery, as the battery wont accept a charge at the same rate as an AGM.
AGM is better for winching/DC to DC charging applications because it is more likely to recover quickly from the demand placed on it and can be discharged more than Lead Acid (80% vs 50%).
A high output alternator should help to eliminate load based voltage drops, but alternator output Voltage is still controlled by the ECU.
Land Rover LR3 ECU alternator control seems to be set to Lead Acid chemistry judging by the voltages we see.
We can prolong the life of AGM by topping it up with an external charger every two weeks to one month, but the charging system in the LR3 will never fully charge AGM.

Would love to have your feedback!

 

I ran a standard alternator, standard battery and a warn vr10000 winch that I used a fair amount no issues for many years

agm battery standard alternator and no winch had way more issues

 

This was on an LR3 right? Standard battery being Flooded Lead Acid? What's the life you got out of the battery?

 

This is nice for me to read as I'm wanting to add lighting to my LR3 in the near future and really didn't want to deal with adding more output from the charging system...

 

My biggest concern is the DC to DC charger pulling 50A out of the battery constantly. Not sure what the charge rate is on Lead Acid, but 50A is a lot to add to an alternator that has a max output of 150A, especially if the battery is not able to absorb charge at the same rate as delivering 50A extra to a charger.

From what I've read, manufacturers spec alternators with about 10% headroom once worse case scenario is reached by the charging system. 50A is 30% of max alternator amperage.

This is where the AGM could potentially be great with an charge absorption rate of 5x Lead acid.

Unless charging fully (via alternator) will double or triple the lifecycle of AGM, I think the point is moot. Walmart sells Everstart Platinum H8 AGM with 900CCA and 36month warranty for $180, which translates to $60 per year. I may just make peace with the fact that I'll be replacing battery every 3 years.

 

Whoever told you to do that is not someone I would consult for wiring advice..... It is bad practice but if done, the wires must be the same exact length. The reason for it being a bad practice is you are lending yourself to a fire situation under load should one of the wires have a bad crimp, fail, etc. The alt can put out 14.8 under certain conditions, but you normally do not want voltages that high anyway for the health of the electronics. I believe the stock starter/alternator wiring is 1/0 awg or maybe one size below.

Really you are overthinking things. I run a 12,000 lb winch, tons of accessory lights, fridge, water heater, etc, etc..... I never felt the need for an alternator upgrade. But one of the very first mods I did was an aux battery, slightly smaller than starting (not ideal). I have a Blue Sea smart solenoid with dash switch. When winching I will press the override to make sure the aux and main stay connected for some extra winch juice. You always pull winch power from the positive terminal on the starting battery. My wiring form battery to battery is 1/0awg. My starter/alt wiring is still stock. My latest addition is just one 100watt solar panel - this keeps my aux battery very well topped off and sometimes I will flip the smart solenoid when parked to get both batteries to settle. Both my batteries are years old now. Starting battery was put in 2020 and aux was installed 2019 but warranty in 2020. Alternator was replaced with OEM Jan of 2021, I still have the original to rebuild and another new OEM on the shelf as backup - I do a lot of water crossings.....

So I would maybe suggest going with an aux battery first. Once nice thing is being able to jump start ones self (assuming you let the smart solenoid do its thing and auto-disconnect when truck is off).

But why would your DC to DC being pulling 50 amps all the time? That makes no sense. And what are you using it for? Do you already have an aux battery? (FYI, if you run a AUX battery only through a DC to DC you can not use the second battery for jump starting or winching)

 

correct both LR3. The battery was still good when I scraped the truck and is still in use around the shop at 6 years old. I also had multiple off road lights, and fridge

I had at one point 4 hella 500 led lights in the rack, 2 rugged ridge 3” lights in the bumper and 8” warn HID lights on the bumper

 

Thanks for the info DakotaTravler.

The big 3 wiring upgrade is by no means a unique or new thing. This has been done for many years in the Audio Community to cope with the demands of Audio amps on the charging system (we are talking about adding heavy gauge wire). I understand what you are saying in terms of risk, but there is risk in anything we change to our vehicles. The same could be said for adding a roof rack, awning, fuel cans, spare wheel/ RTT to a vehicle that has a dynamic roof weight rating of only 150lbs. The point I wanted to make is that there is no point to adding just the high output alternator if you are going to keep wiring stock.

I would prefer not installing a second (FLA or AGM) battery in the vehicle. I would like to use the available space in the engine compartment to mount my ARB compressor (not ideal, I know), relocate the winch controller, install another battery post for winch, lights and DC to DC charger connection and install needed fuse/relay holders. I am building a battery box (using a condition 1 case) that will house a LiFePo4 battery, inverter and DC to DC charger. This can go into the vehicle when needed and be removed when not needed. I will run the fridge off this, and can also use if for other camping/fishing trips or power outages. This way I can easily convert the vehicle back to a 7 seater when needed - one of the features I like most.

Lack of space to run 2 batteries (in conjunction with what I want to do in the engine bay) was the reason I was looking at a high output alternator in the first place. The DC to DC would draw 50A for a maximum of 2 hours if the 100AH Lithium battery was completely discharged, but even if it was only 25% discharged it would still draw 50A for 30min. My concern is not that I need to provide 50A constantly. My concern is the low ceiling I have with the existing alternator (I have done some more reading on this, and I may have had the wrong info - other sources quote headroom as 30 - 40%) given the fact that I don't want to install a secondary FLA or AGM battery. I may be overcompensating with a high output alternator by thinking about worst case scenarios.

I think I should keep the alternator stock, run the DC to DC as is, and see what effect that has on the battery/alternator's ability to keep up. Worst case, I'll kill a $180 battery by deep-discharging it too often. I carry a fully charged NOCO jump pack in the car at all times, and I can attest that it will jump the LR3 at least 4 times on a charge.

Are you running FLA or AGM for batteries?

 

@ArmyRover Wow, 6 years on a battery! My wife's Rogue has eaten 3 batteries (1 was a warrantee claim) in the 5 years we've had it, so I kinda just assumed it is the norm nowadays.

Did you run everything off the starter battery (no secondary battery)? How long did that battery serve in the LR3?

 

I’m familiar with the big three upgrade, but it has always involved replacing the wires, never heard of running wires in parallel for it - which is a bad idea really given the loads we are talking about. With audio, probably less an issue since the draw is not constant.

Second battery bay would be a rather long run for a winch controller. Lots of additional wiring too that would have to be bumped up in size. So keep that in mind. I mounted my solenoid box to the metal bumper at the wheel well.

You 100 ah lithium will be able to run a 12v fridge for days. I doubt if you will ever totally drain it. Solar may be a way to take the edge off. Even my small 100 watt panel keeps all my stuff running during the day.

My batteries are flooded and I top them off time to time.