Lithium Starting Battery With 210 Amp Alternator

[DonTom]

I have been thinking about going all lith in this motorhome.

This 2022 Entegra Coach Vision 27A has a group 25 battery, a Motorcraft BXT-65-750 as stock.

And this motorhome has a 210-amp alternator.

The XV6500 is a group 25 lith engine starting battery, but it says NOT for use with alternators that are above 150 amps.

Why is that an issue? This XV6500 battery is higher voltage than lead acid, I would expect this lith battery to draw less current, not more.

"Usage strictly limited to alternators 150A or less!"

XV6500 battery specs and info here.


-Don- Tonopah, NV

 

[bigbAZ]

But aren't lithium batteries are capable of drawing more current due to their lower internal resistance, which is why they also charge faster than LA? Maybe they don't want the liability of your wiring getting overheated?

 

[bigbAZ]

FWIW you can buy drop in LiFeP04 starting batteries for Mercedes Sprinter and Sprinters come standard with 180 and 220 amp alternators. Does the battery you are looking at have an internal BMS (I don't see it in the description)? What about running it with a 150 amp battery fuse like a MRBF or an ANL?

PS Is 670 CA enough for your rig?

 

[DonTom]

But aren't lithium batteries are capable of drawing more current due to their lower internal resistance, which is why they also charge faster than LA? Maybe they don't want the liability of your wiring getting overheated?

Capable, yes. But you need to have the higher voltage than the battery for it to charge at all. They do not charge faster unless you give them more amps to charge with by raising the voltage well above the battery voltage. And this lith battery has a higher voltage than a lead acid.

That is why I make no sense out of this, but I have no idea what I am not seeing in this "strict limit" for an alterator.

-Don- Tonopah, NV

 

[DonTom]

PS Is 670 CA enough for your rig?

The stock LA battery is 750 CCA, I would think 670 CA is close enough to not be an issue, especially with the higher voltage from the lith. in reality, the engine will probably crank even faster after the first second or so.

-Don- Tonopah, NV

 

[DonTom]

FWIW you can buy drop in LiFeP04 starting batteries for Mercedes Sprinter and Sprinters come standard with 180 and 220 amp alternators. Does the battery you are looking at have an internal BMS (I don't see it in the description)? What about running it with a 150 amp battery fuse like a MRBF or an ANL?

The BMS is probably different in a lith engine starting battery. But your question probably gave me the answer I was looking for:

"Alternator Compatibility: Vehicle alternators are designed to charge lead-acid batteries and may output voltages (up to 15V–16V) that trigger a lithium BMS to shut off charging, leading to the aforementioned electrical damage"

IOW, a more powerful alternator will raise the voltage more when no load from the battery and can damage things when the BMS disconnects.

I assume that is the answer. Probably best that I just stick with a stock LA battery for engine starting.

-Don- Tonopah, NV

 

[DonTom]

I just did an AI search on the BMS for a lith starting battery:


"Yes, the BMS in a lithium starting battery is specifically designed to be different from one in a standard deep cycle lithium battery.
The key difference lies in its high-current capability:

• Starting Battery BMS: Engine cranking requires massive bursts of current (hundreds of amps). A lithium starting battery's BMS is engineered with high-amperage MOSFETs to handle these extreme, short-duration cranking loads without tripping and disconnecting. For example, the Blue Heron 105Ah Dual Purpose battery's upgraded BMS can supply a 250A burst for 10 seconds.
• Deep Cycle Battery BMS: These are designed for sustained, lower-current discharge over long periods (e.g., powering RV appliances). Their BMS is typically rated for much lower continuous and peak discharge currents. If used to start an engine, the high current demand would likely cause the BMS to trip, cutting power and potentially leaving the engine unstarted.

In essence, a starting battery BMS is built like a heavy-duty switch to manage the intense power surge of cranking, while a deep cycle BMS is optimized for long-term, stable power delivery and energy management. "

 

[DonTom]

While I was using AI, I also asked about the 150 amp limit:

The 150-amp "limit" for a lithium starting battery is not a strict rule for the battery itself, but a safety guideline to protect the vehicle's alternator.

Lithium batteries have extremely low internal resistance. When connected directly to an alternator, they act like a "power sponge," attempting to draw the alternator's maximum possible output continuously. Most automotive alternators are not designed to run at 100% capacity for extended periods.

• Overheating Risk: Sustained high-current charging (e.g., over 70-80% of the alternator's rated output) can cause the alternator to overheat and fail.
• Continuous vs. Peak: A 150-amp alternator might handle a brief 150-amp load, but it cannot sustain that peak output safely while the engine is running. The "limit" ensures the alternator operates within a safe, sustainable range (often 50-70% of its rating).

Therefore, the 150-amp figure is often cited as a practical maximum for alternators charging lithium batteries without additional protection. To safely use a larger alternator or ensure longevity, a DC-DC charger is recommended. This device acts as a current limiter, protecting the alternator by only drawing a safe, pre-set amount of power (e.g., 80 amps) from it, even if the lithium battery could accept more.

 

[DonTom]

I will now probably look into using a DC2DCC in this, now that I have the reason for the limit, which was much like your guess for the "lower internal resistance" which I did not expect when the lith battery voltage is higher than a LA battery. But probably still draws too much current when the charge voltage raises from a BMS shutdown or whatever.

The DC2DCC looks like a great idea if I am going to decide on doing such and not just stick with the LA.

I will check to see how easy it is to get to the battery charging wire in this and if possible, I will then get myself an 80-amp or so DC2DCC.

. . . I cannot find 80 amps with a quick search, but I assume this will work.

-Don- Tonopah, NV

 

[Brad Buchanan]

Most automotive alternators are not designed to run at 100% capacity for extended periods.

Actually they are rated for continuous duty.

 

[bigbAZ]

I've been very pleased with AGM. I keep all my AGMs on maintainers and get long lives with them. The one in the MH is connected so that every time I am on shore power the maintainer is working. I like to keep the chassis battery on some sort of charging while camping since it powers the slides, awning and recliner elevators. Plus I am always plugged in at home.

On an RV you have a backup if the chassis battery goes bad, you can always jump it from the house.

 

[triplethreat]

I will now probably look into using a DC2DCC in this, now that I have the reason for the limit, which was much like your guess for the "lower internal resistance" which I did not expect when the lith battery voltage is higher than a LA battery. But probably still draws too much current when the charge voltage raises from a BMS shutdown or whatever.

The DC2DCC looks like a great idea if I am going to decide on doing such and not just stick with the LA.

I will check to see how easy it is to get to the battery charging wire in this and if possible, I will then get myself an 80-amp or so DC2DCC.

. . . I cannot find 80 amps with a quick search, but I assume this will work.

-Don- Tonopah, NV

Don, I have no idea what the voltage cap is for a LFP Starting battery, but the "normal" LFP batteries' BMS has a voltage cutoff of 14.6 volts....maybe 14.7V. Alternator output voltage might be an issue, but like I said, I have no knowledge of the LFP starting battery's BMS specs.

 

[DonTom]

Don, I have no idea what the voltage cap is for a LFP Starting battery, but the "normal" LFP batteries' BMS has a voltage cutoff of 14.6 volts....maybe 14.7V. Alternator output voltage might be an issue, but like I said, I have no knowledge of the LFP starting battery's BMS specs.

The lith starter battery is ~0.55 VDC above a LA starting battery at the same SOC. I assume it's always around that much above the LA for the BMS and charging, etc.

I will be using a DC2DCC on the starter battery as well as the house batteries anyway, if I go with my plan for changing to lith on each.

Just as I did with the 300 AH Lifep04 battery I added in this for my toys (ham radio, & high power stuff ,MW oven, etc., for where I cannot run the genny). So far, I left the stock stuff as stock, which is all LA and I still could. I am undecided at this point if I want to bother. Even new LAs will probably outlive me anyway.

-Don- Tonopah, NV

 

[ButchW1]

Interesting topic.... I wonder when vehicle manufactures will do away with LA batteries, and what they will go to... Will 14.?V be the new norm as apposed to 12V...
Butch

 

[DonTom]

Interesting topic.... I wonder when vehicle manufactures will do away with LA batteries, and what they will go to... Will 14.?V be the new norm as apposed to 12V...
Butch

I expect even the Lifepo4 batteries will soon be gone when then new solid state batteries come out which will probably be before the end of this year. And the price of all other batteries will probably drop in price even faster than they have been.

-Don- Tonopah, NV

 

[Lou Schneider]

The XV6500 is a group 25 lith engine starting battery, but it says NOT for use with alternators that are above 150 amps.

Why is that an issue? This XV6500 battery is higher voltage than lead acid, I would expect this lith battery to draw less current, not more.

"Usage strictly limited to alternators 150A or less!"

XV6500 battery specs and info here.


-Don- Tonopah, NV

Most likely the battery's BMS doesn't monitor current flowing in or out of the battery to eliminate the voltage loss (and heat) inherent in a current shunt so it can provide the rated 670 amps of starting current. That implies a total internal resistance of 0.001 ohm or less to avoid a 10% voltage drop at full current. And 150 amps is the maximum allowable charging current.

 

[DonTom]

Most likely the battery's BMS doesn't restrict current so the battery can provide the high starting surge. And 150 amps is the maximum allowable charging current.

Yep, that makes perfect sense.

The 60-amp DC2DCC should take care of that issue.

-Don- Tonopah, NV

 

[DonTom]

I am leaning towards keeping the starter battery as lead-acid, but changing the two 6V house batteries (220 AH) to two 200 AH (<400 AH total>12V lifep04 in parallel with a Victron DC2DCC at 30 amps). I do not want to put much load on the alternator, or I would consider the 60 amps. I can always use the lith converter from the Genny if I want a larger faster charge for the house batteries, which I doubt I will ever need.

I am not sure if changing the starter battery from LA to lith is a good idea for several reasons. The norm is for starter batteries to change the charge rate as required which will not happen at a steady 60 amps from the DC2DCC, which is only around 800 watts or so. So if the A/C, lights and other stuff is on that runs from the engine battery, it may not keep up at 60 amps from the DC2DCC.

-Don- From Strawberry Hill (a restaurant in Tonopah, NV).

 

[DonTom]

Most automotive alternators are not designed to run at 100% capacity for extended periods.

Actually they are rated for continuous duty.

That sounds like a contradiction to me.

Or did you leave the word "not" out in the second sentence?

-Don- Auburn, CA

 

[Brad Buchanan]

That sounds like a contradiction to me.

Or did you leave the word "not" out in the second sentence?

-Don- Auburn, CA

it was supposed to be a quote.

I actually worked with a couple of companies in Michigan that were rebuilders.

Almost all were designed for continuous duty.

Now with the chinese copies....who knows.