Drop-in Lithium Engine Start Battery?

[sailorbenji]

Does such a thing exist?

The reasoning is our boat is used by quite a few people, some more technical than others. It also sometimes has weeks, even a month or two, between uses.

It's very easy for someone to leave the engine breaker on (engine has ECU drain etc), and when we return, the engine start battery is very low, even dead. This has caused at least a couple of lead-acid battery failures.

The easiest answer would be to ensure the engine breaker gets turned off, but even with the amount of times I've stated this, and even with the amount of red stickers around the boat stating what to do; it seems an impossibility to some.

I'd be interested, if such a thing exists, to use a drop-in lithium replacement, my primary driver being that the BMS would/should prevent the battery being drained to the point of damage.

So, does such a thing exist indeed, or not?

 

[RogerJolly]

Not found casually googling. More available for motorcycles. Maybe it's to do with getting the BMS beefy enough to handle the current.

 

[Sea Change]

LiFePO4 cells are generally limited to a discharge rate of 1C, and the BMS packaged inside the battery will almost always have the same limit or lower.
So this means that to replicate e.g. 600CCA, you need an enormous 600Ah LFP battery.
It's just not necessary, when a cheap lead acid will do the job perfectly.

You could achieve what you want much more effectively, easily, and cheaply, using some form of voltage sensing relay to prevent the start battery from becoming too deeply discharged.

 

[sailorbenji]

LiFePO4 cells are generally limited to a discharge rate of 1C, and the BMS packaged inside the battery will almost always have the same limit or lower.
So this means that to replicate e.g. 600CCA, you need an enormous 600Ah LFP battery.
It's just not necessary, when a cheap lead acid will do the job perfectly.

You could achieve what you want much more effectively, easily, and cheaply, using some form of voltage sensing relay to prevent the start battery from becoming too deeply discharged.

Thanks, I suspected as much. I'm familiar with lipo batteries in the RC world having extreme discharge rates of 50C and upwards, but less familiar with LiFePO4 characteristics. Of course the lips also don't have a BMS integrated.

Could you elaborate on how one would achieve what you suggest in the last paragraph? Is there a baseline schematic for such a set up you've seen somewhere?

 

[Tranona]

Do you not have an emergency start switch to connect the house bank to the engine, or parallel them? Very easy to install if you do not.

 

[Sea Change]

Thanks, I suspected as much. I'm familiar with lipo batteries in the RC world having extreme discharge rates of 50C and upwards, but less familiar with LiFePO4 characteristics. Of course the lips also don't have a BMS integrated.

Could you elaborate on how one would achieve what you suggest in the last paragraph? Is there a baseline schematic for such a set up you've seen somewhere?

The Battery Protect from Victron is one example of how to do this- just wire all your non engine loads through the BP, and set your desired cut off voltage.

 

[geem]

Assuming you have some form of charging for domestic bank whilst the boat is not in use, you could add a DC/DC charger to keep the engine battery charged from the domestic bank.

 

[sailorbenji]

Do you not have an emergency start switch to connect the house bank to the engine, or parallel them? Very easy to install if you do not.

Starting the engine isn't my concern so much as the health of the start battery ongoing, if it flattens (last time was to 3-4V and the battery just wouldn't take a charge after that).

 

[sailorbenji]

The Battery Protect from Victron is one example of how to do this- just wire all your non engine loads through the BP, and set your desired cut off voltage.

The problem is, it IS an engine load (if left on accidentally) that drains the battery. Presumably a Battery Protect wouldn't take the A required during cranking? If it could, it's an option.

 

[Sea Change]

The problem is, it IS an engine load (if left on accidentally) that drains the battery. Presumably a Battery Protect wouldn't take the A required during cranking? If it could, it's an option.

Yes, you can't run a starting current through a BP.
What is the load that you're concerned about?

 

[sailorbenji]

It's a CR diesel, so if people inadvertently leave the engine breaker on, the ECU etc. drains the battery, surprisingly quickly!

 

[Sea Change]

It's a CR diesel, so if people inadvertently leave the engine breaker on, the ECU etc. drains the battery, surprisingly quickly!

Ah gotcha.
What size is the breaker? Does it handle the whole start circuit, or just the ECU etc?

 

[sailorbenji]

Ah gotcha.
What size is the breaker? Does it handle the whole start circuit, or just the ECU etc?

I can't remember off the top of my head, the breaker itself is a Blue Sea Remote ML-remote battery switch - rated at 500A....I can't imagine why it would be that beefy if it wasn't handling the whole start circuit?

 

[CaptSmithers]

Does such a thing exist?

The reasoning is our boat is used by quite a few people, some more technical than others. It also sometimes has weeks, even a month or two, between uses.

It's very easy for someone to leave the engine breaker on (engine has ECU drain etc), and when we return, the engine start battery is very low, even dead. This has caused at least a couple of lead-acid battery failures.

The easiest answer would be to ensure the engine breaker gets turned off, but even with the amount of times I've stated this, and even with the amount of red stickers around the boat stating what to do; it seems an impossibility to some.

I'd be interested, if such a thing exists, to use a drop-in lithium replacement, my primary driver being that the BMS would/should prevent the battery being drained to the point of damage.

So, does such a thing exist indeed, or not?

I have 3 12v 250 ah lifepo4 wired in parallel and I was sick of my DC to DC charger draining my battery so I got rid of my lead batteries and my DC to DC. I have the lithium connected straight to my 250 Yamaha outboard. And these are just generic lifepo4. On Amazon today I just bought another 300 amp hour 12 volt lithium for $269. I've played around with a battery load tester and you can crank near anything with even one of these.

 

[CaptSmithers]

I have 3 12v 250 ah lifepo4 wired in parallel and I was sick of my DC to DC charger draining my battery so I got rid of my lead batteries and my DC to DC. I have the lithium connected straight to my 250 Yamaha outboard. And these are just generic lifepo4. On Amazon today I just bought another 300 amp hour 12 volt lithium for $269. I've played around with a battery load tester and you can crank near anything with even one of these.

Also, one time I left the fridge on for a month and my BMS went asleep I just used a portable jump starter to awaken it and then I was able to start the motor.

 

[Sea Change]

I have 3 12v 250 ah lifepo4 wired in parallel and I was sick of my DC to DC charger draining my battery so I got rid of my lead batteries and my DC to DC. I have the lithium connected straight to my 250 Yamaha outboard. And these are just generic lifepo4. On Amazon today I just bought another 300 amp hour 12 volt lithium for $269. I've played around with a battery load tester and you can crank near anything with even one of these.

What CCA does your outboard require?

 

[kingfisher]

Put a solar panel somewhere? Even the smallest solar panel will cover the drain from an engine ECU left on.

 

[CaptSmithers]

What CCA does your outboard require?

Listed between 500 and 800 I think. I've tried torture testing all my lithium batteries with a load tester and they all put out like 900 cranking amps even when the BMS says it's 150 or 200AMP with no voltage drop

 

[Jes1]

Battery capacity is not all what matters. Batteries are designed for specific applications. A starter battery does have another internal construction than a emergency backup battery. That's applicable for both leadacid and LFP batteries.
Just compare LFP peak current specs of an EVE cell against a Winston cell.
Drop-in batteries are black boxes using unknown (mostly cheap) components and often without documentation and/or incorrect documentation.
And equal to owners computer experiences, they work either "perfect" or are a "bag of shit" (which can vary in an instance).
Using plug-in LFP without knowing their specification and/or limitations, without knowing your demands might well end up in a nasty surprise at a moment that you cannot affort that to happen.
Keep in mind that a 80A DC starter motor will surge for 300 .. 500 A inrush current (tripping the BMS or slowly damaging the LFP cells and/or BMS FET's in the plug-in battery).

 

[PaulRainbow]

Listed between 500 and 800 I think. I've tried torture testing all my lithium batteries with a load tester and they all put out like 900 cranking amps even when the BMS says it's 150 or 200AMP with no voltage drop

Your BMS is rubbish then. One of the purposes of the BMS is to limit current draw to a safe level for the batteries. If you want your batteries to last well, current draw is typically best to be 1c at the most.