18650 DIY powerwall 48v

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Fukuokian said:
I wonder if a reptile heating pad would work better for direct contact to the batteries? I think they have their sensor built in, so it regulates the temperature quickly. (Not sure about this though.)

You could experiment with the placement of your sensor (maybe closer to the pad). Thanks for posting your journey... I'm watching closely, cuz I want to have heating and ventilation cooling when I get my battery together.

Btw, those temperature controllers work great for vide sous cooking. I use one hooked up to a slow cooker... Amazing steaks from lower quality meat! Perfectly cooked every time (you do need to sear it after though, but that's quick and easy.).
Click to expand...
Thanks.
The steak looks very good. 😋

The original leaf battery had some thin aluminium plates close to the heating pads. I'll use the plates between my battery and my 48v heating pads so it spread the heat and the pads are not in direct contact with the battery.
 
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How can I find out the specs on this original leaf heating pad?

How many volts and watts it's operating at?

20251124_140626.jpg
 
I don't know if this info is accurate... But this is what I found:
TypeResistive heating pad/element (PTC or fixed-resistance); integrated into battery stack modules (front/right-side typically)
Voltage350–400V DC (drawn from high-voltage traction battery via BMS control)
Power Output300W (nominal; activates in bursts to avoid excessive drain)
Current Draw~0.75–0.85A at nominal voltage (low draw to minimize range impact)
Resistance~400–500 kΩ (cold state; self-regulates if PTC-type)
Activation TemperatureAutomatically engages at ≤ -20°C (4°F) or -30°C (-22°F) in some variants; deactivates at ≥ -10°C (14°F)
Operating Temperature Range-40°C to +60°C (battery pack ambient); self-limits to prevent overheating
Dimensions (Approx., per Element)150 mm x 100 mm x 5 mm (thin pad; multiple elements per pack, e.g., #1/#2 positions)
Weight~0.2–0.5 kg (per element; total assembly ~1–2 kg with wiring)
MaterialFlexible silicone rubber pad with embedded nichrome or PTC ceramic coils; aluminum substrate for heat transfer; HV-insulated wiring
LocationEmbedded in battery modules (under vehicle floor; right/front stack); controlled by Li-ion Battery Controller (LBC/BMS)
CompatibilityNissan Leaf ZE0 (2011–2017, 24/30 kWh packs); optional in AZE0 (2018+, 40 kWh); not standard in 62 kWh packs (software heating instead)
Activation ConditionsAutomatic via BMS when unplugged and temp threshold met; requires 12V battery power for LBC; does not activate while charging/driving (natural heat suffices)
Common Fault CodesP0A08/P0A0A (battery heater circuit); B2D00 (thermal management); symptoms include reduced regen braking, slow charging, or low power in cold
Replacement NotesHV safety required (isolate pack, use Class 0 gloves); cost ~$150–$300 for OEM element; full pack access needed (labor-intensive); TSB NTB13-021 covers cold-weather diagnostics


Additional Details​


  • Function: Warms battery cells directly to >10°C for optimal performance, improving charge acceptance (e.g., enables DC fast charging at cold temps) and preserving ~20–30% range loss in sub-zero conditions. It draws from the HV battery, so it reduces usable range slightly (~1–2% per hour active) but prioritizes longevity over immediate driving.
  • Why It Fails: Thermal fatigue from cycles, wiring corrosion, or BMS relay issues; common in high-mileage cold-climate vehicles. No heat generation while parked warm leads to quicker cooldown.
  • Maintenance: Monitored via NissanConnect app (warmer status) or OBD tools like LeafSpy. In models without physical heaters (e.g., 62 kWh), the BMS uses low-level cycling to generate internal heat, drawing ~100–200W indirectly.
  • Evolution: Early 2011–2012 models had basic 300W pads; 2013+ added multi-element setups. By 2018, Nissan shifted to passive/liquid-cooled designs with optional preheat via app-scheduled charging
 
Heating pads... this might be why @Dala suggested a full Leaf EV pack for my potential off-grid property scenario when I posted about LTOs as a way to address low temps when I only visit once every 6 months. As I posted on my thread, I'm back to 18650 and will do a mini-split if it comes to it.
 
Ok so this is a 350–400V DC heating pad.

I wonder if this will make any heat if I connect 48v battery to it?
 
Would a current limiting resistor be required? Edit: it should act on it's own to limit the current right?
 
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Fukuokian said:
You got me thinking... (dangerous I know.) 😉 I've just posted this Solar Thermal Energy storage idea for my battery bank in my thread, but I'll link it here as you might be interested in something I've found. https://secondlifestorage.com/index...f-48v-off-grid-solar-project.12890/post-94414
Click to expand...
Interesting idea you have there with Solar Thermal Energy. 👍 Especially since you already have the insulated refrigerated box. My battery is in a metal cabinet but it's at least insulated.
 
I connected Leaf battery in parallel with the 18650 battery. Both where 3.931v

Still there was 137w discharging from leaf into 18650 battery. Why is that?

Screenshot_20260303_114025_BMS.jpg
Screenshot_20260303_114036_BMS.jpg
 
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First, congratulations for ongoing progress!

Looks like slightly different voltages - 54.96v vs 55.16v? 137w (~2.5a at this voltage) seems modest. :)
 
Thank you. 🤩

Yes, but the strange thing is that when the two batteries was not in parallel the voltage was almost exactly the same; 3.923v
 
Just because your meter shows the same voltage doesn't mean that the cells chemical state are exactly the same level. This is one of the major reasons that it's suggested to connect a lot of cell-groups in parallel and leave them that way for about a week before you connect them in series to make the battery. This allows for an absolute balanced battery packs.

The same thing happened when I connected my 2 LFP batteries together. They were at the same "voltage", but when they were connected there was actually close to 30A flowing from one battery into the other, even though they never changed voltage during this time. It was weird seeing zero deltaV still flow current.

OffGridInTheCity said:
First, congratulations for ongoing progress!

Looks like slightly different voltages - 54.96v vs 55.16v? 137w (~2.5a at this voltage) seems modest. :)
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Yeah but the flow is backwards from what should be, based on what is shown. The current should flow from the 18650->Leaf, but it's going Leaf->18650. ;)

But in this case, what's odd is that current is flowing out of the lower voltage battery into the higher voltage battery. What this tells me is that you need to disconnect the batteries and with a DMM verify the voltages of both batteries, and then calibrate the BMS to read what the DMM says. I'm gonna guess that the BMS is slightly out of calibration. All 3 of my JK BMS's needed some fine tuning to get them accurate. This also included the current flowing as well. I used a DC-rate clamp meter to measure current and recalibrated the BMS accordingly.

You can adjust those settings on the 2nd page (settings at the bottom) after unlocking by entering your passcode. Which you won't be able to change until you update the default password which it looks like you haven't done yet :p
 
I second the congratulations! (y) You've doubled your powerwall! 30kWh.

With regards to the reverse flow than what's expected, where is the BMS physically located? Is it closer to one bank than the other?
Same question for the charger... it might also have to do with wire resistance.
 
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Thank you. 😊

Yes I was thinking it could have something to do with wire resistance. Each BMS is close to their respective battery bank, but the wire length from BMS to the breakers are not equal.

Good point Korishan. It seems I have to recalibrate the BMS. Maybe that helps. Thank you! 👍
 
I calibrated the voltage on the JK BMS. It seems to be in the right ballpark now. Thank you Korishan. 👍

When trying to calibrate the current flowing with my clamp meter, it didn't work. In the end I discovered I used an AC-rated clamp meter. 😆
I've now ordered a DC-rated clamp meter.
 
kje said:
When trying to calibrate the current flowing with my clamp meter, it didn't work. In the end I discovered I used an AC-rated clamp meter. 😆
I've now ordered a DC-rated clamp meter.
Click to expand...
Lol yeah that kinda makes a big difference 😜
 
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