Ditto that I killed my Odyssey $250 AGM 950CCM battery in less than a year I believe was partially the fault of the high output alternator I installed from Quality Power.
The stock alternator on idle generates 14V (Denso) you need the voltage to drive battery charging. On idle 500-1000 the Quality Power High Amp alternator I installed (250AMP) drops to 13.1 Volt and that would take forever to charge any large battery with (for that you rather want say 14.5 Volts for some healthy charging). Everything above 12.9 Volt will charge a battery but it will take forever and when your in a hot climate or say on a hot day with the engine running the voltage needs are even higher for das acids batteries.
So what you have to discuss is not only Amps but also Voltage! So I changed my battery to a regular flooded one which take last about ~0.5 Volt lower charging Voltage than AGM and might be more digestible with my after market alternator. If I **** that battery say in 1-2 Years I'll install the OEM Denso type alternator.
My recommendation is if you don't need the extra AMPs don't install a high output alternator. I installed mine because I have a winch that can draw up to 500AMPs so figured a good alternator would help support the battery and stop it from completely draining.
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, DC to DC charger 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!
