OK gang. I cannot figure out why my lithium battery suddenly goes from ~60% charged to 0% charge overnight. I had the first battery replaced with a brand new lithium battery and the same issue is happening. I will post pictures later, but the only thing I can think of is the small draw on the battery while the cart is off from the lights on the dash. Although, that would not explain why the battery holds a charge until around 60% and then goes to 0% overnight.

I really don't want to bother the battery guy with replacing it a second time if it has something to do with my cart and the way that it's wired. Any ideas what could cause this sort of battery behavior outside of the battery itself malfunctioning?

To isolate the issue, disconnect the battery. That will determine if it's the cart or the battery.

Dumb question
Is it plugged in overnight?
Why are there any lights on overnight or when not in use?

The battery isn't plugged in overnight. I have it wired where the accessories don't turn off with the ignition of the cart.

Example: the headlights and radio can be on while the cart is off. I'm not sure if this has anything to do with battery lifespan since the accessories are off and my app shows no draw on the battery.

Parasitic drain you will have to chase with a multimeter. Look for a voltage where there should be an open across a switch or relay, or a current that should not be present.

If the battery's app is saying there is no draw that to me would indicate something wrong in the BMS of the battery but hunting down a parasitic drain would help confirm that.

Would the slow drain like that lead to a dramatic 69%->0% overnight?

Up to that point it holds for days and weeks

And we're saying I've somehow received two bad batteries when the battery dude said he hasn't experienced my specific problem before. I'm thinking something else is off. It will hold the charge until it gets around 60-70% then it goes to 0 overnight.

I'm going to guess your remaining charge indicator isn't accurate or itself is somehow the draw.

Could be inaccurate I suppose. But I don't have a physical hardware indicator; I use the app only.

Right, perhaps my wording is wrong, I'm not sure what all counts as part of the "BMS" but I suspect you are getting flawed data or there is some sort of battery cell protection kicking in or something. Something within the software on the battery that controls charging and discharging it.

What brand/model battery is it? There are some pretty active golf cart forums out there, you might try posting there.

It's a 105ah Allied brand battery. 48v

I'm on buggies unlimited but it's not as fun as TexAgs

Disconnect ground lead and put multimeter between lead and ground post to check for amps.

I think there is a bad cell in the battery or it needs balancing.

What is balancing? I have the app and each cell appears within .009 volt differential and no bad cells

NWE said:

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What is balancing? I have the app and each cell appears within .009 volt differential and no bad cells

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I assume the battery is fully charged right now? You rarely see cell voltages that tightly balanced on a depleted battery.

Each lithium battery cell has strict voltage limits so a computer (Battery Management System) constantly monitors each cell and disconnects the battery when any cell reaches its full or empty voltage limit. Balancing is a process where (usually) the cell with the highest voltage is shorted to ground (through a resistor) when charging to keep all the cells within a tight range when fully charged.

My thought was that If one cell is weak, say has a capacity of 40Ah instead of say 100Ah like the rest, then when your battery is discharged from 100% to 60% the weak cell will be fully depleted and the state of charge indicator would jump from 60% to 0%.

This is because the state of charge is calculated by counting the amps going into or out of the battery (and not the voltage). But once the BMS shows one cell is fully charged the SOC is reset to 100%. And when the first cell shows it is depleted, the SOC will immediately reset to 0%.

It's also possible but unlikely that the BMS has the wrong Ah capacity which would show a similar signature.

Yes it's fully charged now. Thank you for explaining that

If your cells are that tightly balanced, the odds of having a bad or significantly diminished cell is very low. Keep chasing sneak circuits as recommended above. Those are the most likely source of your issue.

But keep a close eye on the cell voltages when the battery SOC drops below 60%. If the cells start diverging, the lowest cell may not have the same capacity as the rest. Or instead of a diminished cell, the entire battery capacity may be diminished through age and cycle wear.

if this has happened with 2 different batteries, my bet is you have something wired wrong (a short somewhere). I'd also bet your BMS is shutting the battery down to protect it.

I have a 36V EPOCH lifopo4 100ah battery in my golf cart and I've let it sit 'on' (no lights though) for a week and it only took it down a few percent.


you have a 12v buck converter on there? or maybe a separate 12v distribution/fuse box? I'd start there.

Here is my set up

Here's my setup - yes I have a 12v reducer. I included screenshots of 100% and 0% with Individual cells shown. I think you might be into something with the cheap reducer I got on Amazon causing issues. It connects to a block where I can add accessories. I also have a 5 switch on the dash for lights that is connected to that accessory panel connected to the reducer.

MouthBQ98 said:

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Parasitic drain you will have to chase with a multimeter. Look for a voltage where there should be an open across a switch or relay, or a current that should not be present.

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he's right. gonna have to chase it. no way (99.9% sure) you have the same problem with 2 different batteries.

I tend to agree. Just to be clear, it doesn't slowly drain. It gets to 70% like normal then ends up at 0 the next morning

NWE said:

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I tend to agree. Just to be clear, it doesn't slowly drain. It gets to 70% like normal then ends up at 0 the next morning

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the nights that it goes to 0....do you turn the battery off or do you leave the switch (the power button the battery) on?

Also are all your external devices (LED lights, radio, whatever) fused or are some just hard wired with no fuse? If you have something not fused...I would definitely start looking there.

Battery stays on always. The switches are NOT linked to ignition but it doesn't look like they drain it daily. Only issue is when it gets to 70%.

Good question about fused. I THINK everything is on a fuse but I need to check

NWE said:

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Battery stays on always. The switches are NOT linked to ignition but it doesn't look like they drain it daily. Only issue is when it gets to 70%.

Good question about fused. I THINK everything is on a fuse but I need to check

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the only other thing I would recommend is to disconnect everything except for the golf cart and see if that drains your battery over night. If that doesn't do it, it's one of your lights/LEDs/radio, etc. I know the buck converters do drain the battery some every day so you might either want to physically turn off the battery every time you're done using it, or at least add a switch for that, but I doubt its that 12v converter...but you never now. Could be a cheap Chinese one with some bad/faulty soldering.

Bump

I'm not getting the drain on the battery when I turn it (the battery) off between uses. Only when I leave it on and the total charge goes below 70%. It will overnight drop to 0% as what I think is a BMS function.


Want to have switches and stereo on ignition switch on my golf cart.

Currently:
- 12v Reducer is connected to lithium battery
- fuse box/accessory block (12v) connected to 12v reducer
- stereo and dashboard switches, one positive one negative wire to and from the single switches Mount (underglow, headlights, spot light, cabin LEDs) are connected separately to the fuse box/accessory block

The ignition switch is not Involved in any of the accessories so they can work while the cart ignition is OFF

I'm getting parasitic drain of my battery this way and want the stereo and accessories linked to the ignition switch.


I'm posting this on buggies page too but always like the feedback I get from y'all.

NWE said:

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Bump

I'm not getting the drain on the battery when I turn it (the battery) off between uses. Only when I leave it on and the total charge goes below 70%. It will overnight drop to 0% as what I think is a BMS function.


Want to have switches and stereo on ignition switch on my golf cart.

Currently:
- 12v Reducer is connected to lithium battery
- fuse box/accessory block (12v) connected to 12v reducer
- stereo and dashboard switches, one positive one negative wire to and from the single switches Mount (underglow, headlights, spot light, cabin LEDs) are connected separately to the fuse box/accessory block

The ignition switch is not Involved in any of the accessories so they can work while the cart ignition is OFF

I'm getting parasitic drain of my battery this way and want the stereo and accessories linked to the ignition switch.


I'm posting this on buggies page too but always like the feedback I get from y'all.

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did you ever disconnect everything and leave the battery on over night and see if the problem goes away? I would pull all the fuses and make sure the battery itself can stay on and not drain over night, then one by one add back a fuse/circuit until you identify the problem. I can almost bet you have a short somewhere. Maybe a nick'd wire shorting out, or some contacts that are shorting out.

Good chance that one of your accessories, probably the radio, has a capacitor inside it. My guess is that maintaining that capacitor is depleting the battery.

The "it only happens below 60-70%" is irrelevant. One of the accessories you added has a parasitic draw.

Just turn everything off overnight and isolate the battery like it was intended to be.