Can I mix lithium battery with lead acid?

i am going the exact same route myself.
for safety, i am planning to have the headway pack 100% open (disconnected) while the vehicle is off.
i am not planning to use a charge controller on my set-up... personally.
the headway pack would only be connected to the vehicle's alternator/other battery when the car is on, for me.

i am thinking either high current manual mechanical switches or.... high current electrical relays.
i am planning to use a switch on both power and ground connection for the headway pack, to full open it from the vehicle.

Let us know what you end up doing, post pics and details how the build is going.
i think a lot of people just use the cell voltage balancing circuits to try to keep the voltage equal on the different series battery strings.
for car audio applications, i believe people do not "typically" use full charge control modules.

@quickaudi07 uses headway pack, you can search for his setup. i believe he is directly connected into his oem electrical system.

@jacob_whit what vehicle will this be going and what's the alternator capacity?

jacob_whit said:

Hey guys, I am looking at building a 16ah headway lithium battery to put in trunk as primary battery for audio system. My other battery would be lead acid to power car electrical.
If I have a charge controller on lithium, how should I connect the two batteries?
Would an isolator work? Or would I need to use a separator? I understand mixing battery types is generally recommended against. I also realize lithium has higher nominal voltage than lead acid.
If there is a better alternative than using lithium in trunk, I'm open to all recommendations.

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you are correct the cells have no built in protection,... raw.
it seems like they can do 80A continuous charge per cell,
and 200A continuous discharge per cell.
i assume they can tolerate higher level for a shorter time.

"USED HEADWAY 38120 HP 3.2V 8AH LIFEPO4 BATTERY"

you think the batteries would get so depleted they would draw that much from alternator?
... i guess it depends on how much / how long current is drawn off of them....

you have any charge controller systems you like / recommend?

the stuff you are saying could happen, but not guaranteed to happen, .... depends on how much current is drawn and the guys alternator charging voltage.

🤷‍♂️

Dark Winter said:

You really should use a battery management module with these. Yes; they are more robust than other lithium chemistries from a safety point of view, but there's other concerns as well.

Without a charge controller, you are likely going to exceed the max charging rate and end voltage on the cells as well as put excess stress on your alternator. Also, I think these are raw cells, without any internal voltage cutoff chips. The result will be reduced cell lifespan; and potentially immediate cell failure upon exceeding the lower discharge limits.

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I don't have any specific recommendations for battery management modules; most of my experience with lithium batteries comes from RC & drones; and a little bit of designing my own devices. RC stuff has the protection/management built into the motor controllers and the charger; and for the latter I would go with whatever was a) in stock at Digikey/Mouser, b) suitable for the battery pack I was thinking about using, and c) in a package suitable for hand-soldering (so, no QFN, LGA, or BGA packages).

If that page is accurate; that's one monster of a cell.

I do think that it could well put that much strain on your alternator; exactly how much will depend on how many cells you have in parallel; and what the state of charge on them is when the alternator's output is connected to them. When they are at a low charge state; to the alternator they are going to look similar to a dead short... depending on how your specific vehicle is wired, you might even blow any main fuse that the alternator has protecting it.

Also; as the main engine starting battery is connected to the alternator, if the lead-acid battery's voltage is above the voltage of the lithium pack, the lead-acid battery going to try to charge the lithium cells - resulting in much more current flowing to the lithium pack than the alternator could put out by itself; and (again, depending on the specific states of charge and how many cells you have hooked up in parallel) probably exceeding the cell's rated charging current (yes, even at 80A/cell - starting batteries can put out a horrendous amount of current, although only briefly).

If, as is proper practice, you put fuses between the main lead-acid starting battery and the wiring going back to the lithium pack, all that current flowing is going to blow the fuse; if you omit the fuse, you'll have at best a melted wiring harness but more likely a car-b-que. 🔥

I say "could happen" because I'm not there looking at the specific car and battery pack. There could always be some factor that I'm not aware of sitting here banging away on my keyboard.

Let me put it this way: Under no circumstances would I install a lithium pack in my car without a protection/management module; and I wouldn't feel comfortable riding in such a car either.

Not recommended, I would suggest to use AGM and have isolator in between if possible depending on what kind of battery you will use. If you go with headway cells, than you be fine.
I ran AGM with lithium side by side without isolator, and now I have AGM with Headway lithium love the extra power!

Safest headway batteries, also they provide power for days! My voltage doesn’t drop below 14.2 volts with music or without!



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from original post, it sounds like @jacob_whit would be making a 16aH ("12V") headway set-up,
so i think he would be going 2x parallel strings of... 4 series cells (8aH ea.) so then 8 cells total.

the resting voltage on these headway cells..... and also the charging voltage range appears to be similar to lead acid.

i think we are agreeing .... just need to size the pack correctly for the draw this guy is expecting & also take into account alternator output voltage.
if you get those things right, and assuming you wire things with correct size wires, etc. this should be a slam dunk?? 🏀

how did you size your batteries when you were making RC stuff/your own designs? what was your methodology?
i believe this is one of the tougher design aspects to get right, i personally think many people just go very large, for safety.

Dark Winter said:

If that page is accurate; that's one monster of a cell.

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yeah you can research them .... specs appear accurate. they are used in industrial applications.

"SUPER BEAST 24v 48ah 1.23kWh - 48 HEADWAY CELLS"