[2024][JaR][Electrical] Confusion around battery chemistry in 2024

[dxulander]

Looking for a suitable upgrade of my batteries, which then of course implies getting into the weeds on the battery chargers (AC charger and solar controller/chargers) to make sure they're appropriate as well.

As-is:
- Battery (starter): Flooded Lead-Acid
- Battery (house): Flooded Lead-Acid
- Charger (AC): Xantrex True Charger 2 20A, charges both banks
- Charger (Solar connected to the starter bank): Morningstar SL-20L-12 (for Flooded Lead-Acid)
- Battery selector 1/2/all/off

To-be:
- Looking to at minimum upgrade house to LiFePO4 (i.e. saves me $500 from having to also upgrade starter to LiFePO4 w/ CCA requirements)
- Victron MPPT controllers (net-new for house bank, replace current for starter bank)
- Isolate the banks w/ Blue Sea Systems 7650

So here's my confusion from reading hours of forums, product specs, etc. And I just can't tell, how much of this is stale because it's now 2024 and technology has evolved, or these are still things we should stick by. The problem statement is I continue to read "don't mix battery w/ different chemistry, bad bad bad, because the charging profiles/algorithms are very different, i.e. 2 stage for LiFePO4 v.s. 3 stage for Lead-Acid variants, flooded, AGM, etc". And my use-case 2 key questions:
- What if I only upgraded house to LiFePO4, and kept the Lead-Acid starter, is mixing really a big deal here?
- Is there a single charging profile/spec that supports both chemistries? I think there is, but looking for some validations.

Then I start reading about the various batteries specs:
https://battlebornbatteries.com/charging-battleborn-lifepo4-batteries/ allows for 3 stages and "A float is unnecessary since lithium-ion batteries do not leak charge, but a floating voltage under 13.6 V is fine. "
https://dakotalithium.com/product/d...r-starter-deep-cycle-lifepo4-battery-1000cca/ allows for "lead acid chargers will work".

Here's the Xantrex True Charge2 spec:


Here's the Victron Solar MPPT charging spec specific for LiFePO4:


Conclusion when I compared to what the 2 chargers (AC and Solar) can supply (i.e. 3 stages and voltage w/ 0.2V +/- variance).
1. Mixing battery chemistries (can I save $500 from needing to upgrade starter bank). It seems like that a "AGM" profile fits both LiFePO4 AND Flooded Lead Acid. The only differences I can tell from the charging profile is Equalization and Re-Bulk voltage (12.5V for v.s. 13.xV). Are these the biggest reasons for "not mixing battery chemistries" especially for chargers?

2. Single charging profile (even if I did upgrade everything to LiFePO4, can I use the same AC charger): I can disable Equalization, but I don't think I can increase the re-bulk voltage, wondering if this is breaking the model here.

 

[Kenneth K]

A lot of stuff here so it's hard to find a starting point....

First, good on you for investigating charging voltages during various charge phases and noting some similarities. BUT, voltage is only one of about 4-5 parameters of a charging profile. I'm no battery expert, but as I understand charging profiles, they are about applying a specific Voltage and Current (= wattage) for a given time, then measuring the battery's reaction to that added Power (= Watts x time) in terms of changes in Resistance and (on most new chargers) Temperature.

For example, after a 130W-hr charge (13V x 10A x 1 hr, or, 13V x 30A for 20 min), and, knowing that is charging a FLA battery (because you told it so), the charger would expect the battery's internal resistance to increase from R0 (initial resistance) to R1. After the second 130W-hr, the charger expects to see R2. With these data points, the charger can judge where along the charge curve the battery is, and about how long to continue charging before moving onto the next phase. If you set the charger to LiFePO4 setting, it expects a different response the these same power inputs. You can't know what the effects of "tricking" your charger will be when it doesn't see the behavior it expects (based on battery type). Maybe it triggers fault codes and stops charging altogether, maybe it plays it safe and reduces to float-charge only (undercharges batteries), or maybe it increases Voltage and Amperage to try to get the behavior you told it to expect (overcharges batteries). Now add two different battery types to the same charger--deciphering the resultant behavior of the battery(s) becomes even harder.

As to your other comments:

- you haven't addressed how you plan to handle alternator charging, so it's hard to get an overall picture of your proposed system. With expensive Li batteries, I think most folks would upgrade to a programmable alternator regulator to optimize charging. Then again, you can only optimize for Li or FLA, not both.

- I'm curious about your assumptions to estimate $500 in Li upgrade costs for a starter battery. These starters are said to consume about 80A (1000W) during start. People tend to dramatically overestimate their CCA requirements (unless, maybe, you plan on sailing in Maine in February, at -30F).

- The Blue Sea 7650 kit is typically for simple boats that are built with only a single battery and basic ON/OFF switch installed. Since your boat is already wired for 2 banks and has an OFF/1/2/ALL switch, it's doubtful you'd need the second switch. Cheaper to just buy the Blue Sea ACR. But,.....

- It's confusing to think of ACRs as devices used to isolate banks. In the factory configuration of your boat, banks 1 and 2 are already "isolated" by virtue of how they are hardwired. The only become un-isolated (paralleled) when the BATT switch is set to ALL. The ACR does exactly the same thing as the ALL switch, but only when it senses voltage above (approx) 13.5V (i.e., a charge being applied).

- How you wish to use your ALL switch or your ACR also depends on how your run your charger leads. If you run both leads of your 2-bank AC charger directly to the terminals of each battery/bank, then the ALL switch or ACR aren't doing anything. If you run only one set of AC charger leads to one bank, then the ALL switch or the ACR will be needed to parallel the second bank during charging. But, again, this is only recommended with similar battery chemistries.

 

[gabriel]

I wouldn’t risk a fire or increase complexity for $500, and I definitely wouldn’t use anything but a charger that’s made to charge lifePO’s with onboard BMS. Either stay with the heavy heaps of lead, or go all lifepo, it’s worth it. I just replaced my single failed 100ah gel for a single 200ah lifepo and one could almost say its light years ahead of all the lead acid technology.

 

[KS Dave]

Have you seen Rod's latest article on Easy LifePo4 Conversion? I'm not an expert here, but it seems what you want to do can be accomplished with a few components added/replaced. This allows you to keep a lead acid start battery and upgrade to LFP for your house bank. It keeps things much cleaner on the alternator charging side as you should be able to use your existing alternator.

- What if I only upgraded house to LiFePO4, and kept the Lead-Acid starter, is mixing really a big deal here?

- you haven't addressed how you plan to handle alternator charging, so it's hard to get an overall picture of your proposed system. With expensive Li batteries, I think most folks would upgrade to a programmable alternator regulator to optimize charging. Then again, you can only optimize for Li or FLA, not both.

This is where the Victron DC-DC charger comes in. It helps you keep your chemistries isolated by charging your house LFP bank from the lead-acid starter battery (which is getting charged from the alternator). You have to dial in the settings, but it's very flexible.

- The Blue Sea 7650 kit is typically for simple boats that are built with only a single battery and basic ON/OFF switch installed. Since your boat is already wired for 2 banks and has an OFF/1/2/ALL switch, it's doubtful you'd need the second switch. Cheaper to just buy the Blue Sea ACR. But,.....

The On-Off-Combine switch is a key element of the mixed chemistry design, but you'll want to buy the switch only (5511e). The BEP 772-DBC would also fit the bill, here.

But, again, this is only recommended with similar battery chemistries.

From my understanding, this is key. An ACR is only to be used if you have two lead acid battery banks. See Making Sense of ACRs

- Is there a single charging profile/spec that supports both chemistries? I think there is, but looking for some validations.

For shore chargers, it's my understanding you'll always want one dedicated to each chemistry. I think you're asking for trouble otherwise.

I recommend the 'Boat Electrical Systems' Facebook group as a good resource for some of your other questions if no one comes out of the woodwork here. This is a common conversation topic recently.

 

[peaman]

This is where the Victron DC-DC charger comes in. It helps you keep your chemistries isolated by charging your house LFP bank from the lead-acid starter battery (which is getting charged from the alternator). You have to dial in the settings, but it's very flexible.

What protection would be available to prevent a heavily discharged house bank from draining a smaller start bank? In reworking my own system, I saw that Blue Sea Systems recommends charging the house bank directly from the alternator, given that the house bank will more often see deep discharge, whereas the start bank rarely will.

 

[KS Dave]

What protection would be available to prevent a heavily discharged house bank from draining a smaller start bank?

There are a couple of protections for this, actually. One is a feature they call 'Engine Shutdown Detection' which will detect if voltage from the alternator has dropped which would indicate the engine is no longer running. It supports both 'Smart' and 'Regular' alternators. The other is an input voltage lockout that will make it stop charging when it detects low charge from the input side (they recommend a setting of 12.5V). Both have to be configured correctly.

In reworking my own system, I saw that Blue Sea Systems recommends charging the house bank directly from the alternator, given that the house bank will more often see deep discharge, whereas the start bank rarely will.

For this product, the manual actually recommends the opposite; it also gives several wiring/config options for different use cases.

 

[Sean Engle]

[2024][JaR][Electrical] Confusion around battery chemistry in 2024​

What's going on with the title of this thread? What's with the bracketed portions? You know you can add tags to any post or thread which will allow them to be categorized together, whereas adding this to the start of the title will obfuscate it in searches...