[Tag]

Hello all! I recently replaced my 12v battery with a 20AH LiFePO 4 battery and wanted to share my experience as well as some valuable lessons learned. I 3D printed an adapter to make the much smaller and lighter battery fit perfectly under the OEM bracket. The only problem is that I purchased a battery that was unable to meet the demand of the Bolt's 12v system. It worked great during the day time. Clicking the key fob at night would turn the headlights on which caused the BMS to shutoff due to excessive load. The solution was to buy a second battery and put them in parallel to support the additional load. This whole situation was made a little tricky by nature of living in Colorado where the temperature regularly drops below freezing over night which means that I had to pay extra for a winterized battery. This added cost is why I cheaped out and went with a 20AH battery instead of the 52AH variant (which costs around $650).

To test the amperage of various features I pulled out the OEM battery and connected it to the battery harness via jumper cables which provided ample room to attach a clamp meter to the positive lead coming off the battery. Anyway, on to the testing:

Standby/Passive/Parasitic Draw	~.2 amps	My meter was fluctuating pretty substantially here, so take this with a grain of salt.
Key Fob Unlock x1 (from locked state)	21, 21.5, 19.28. 18.20 MAX amps
Key Fob Unlock x2 (from locked state)	21.31, 21.87, 21.93 MAX amps
Key Fob Lock (with driver door unlocked)	25.65, 25.91, 25.99 MAX amps
Key Fob Lock (with all doors unlocked)	25.67, 25.16, 25.01, 25.57 MAX amps
Key Fob Lock (second press only to trigger horn)	23.24, 22.05 MAX amps	Only did this noisy test twice so as to not annoy my neighbors.
Tail lights	11.29, 8.81, 8.81 MAX amps	Door left open for test. Salt.
Headlights	24.71, 17.95, 17.75 MAX amps	Door left open for test. Salt.
Headlights Continuous	~17 amps
High-Beams	37.75, 37.83, 29.99 MAX amps	Door left open for test. Salt.
High-Beams Continuous	19-23 amps
Open Driver Door	9.95, 9.97 MAX amps
Drive Door Left Open	~6 amps continuous
Sitting In Car With Stereo On	~10 amps continuous

My 20AH battery has the following specs so two of them in parallel should easily handle all of the conditions I tested above. In hindsight I wish I'd gone with the 52AH battery in the first place.

Maximum Continuous Discharge Current	20 A
Peak Discharge Current	40 A (7.5 s ±2.5 s)
BMS Discharge Current Cut-Off	50 A ±8 A (32 ±8 ms)

 

[Dark-Fx]

The Bolt will exceed the maximum safe voltage of typical LFP battery occasionally. I don't think this is a good idea. The highest I've recorded off the control module PID was 15.524 V. Lots of data points above 15V. Tends to be because lead-acid has a greater need for temperature compensation when they are cold.

You're also not supposed to charge an LFP below freezing.

 

[Tag]

Oh I completely agree that it's not the best idea. With that being said I'm a tinkerer and am willing to take the risk. Lifepo4 should be safe to overcharge to ~16 volts. It's generally discouraged because it only adds ~1% capacity over a 14v charge. Additionally I purchased low temperature winterized batteries which are safe to charge down to -20°C (-4°F).

 

[GJETSON]

Additionally I purchased low temperature winterized batteries which are safe to charge down to -20°C (-4°F).

Any idea how these were "winterized?"

 

[Dark-Fx]

Any idea how these were "winterized?"

The usual suspect is that they have an integrated self-heating element. I don't have practical experience with these types but I certainly wouldn't trust them to be a replacement for a lead acid system where I live. It just gets too **** cold here occasionally.

 

[JClay]

That's really cool! Congrats. I have been wondering when our battery packs will have a small 12V module to power all the electronic systems.
Or maybe since we already have a crazy 400V -> 12V DC/DC converter, we can start to see 5V and 3.3V electronics natively supported rather than adding all that cost for each ECU module to have it's own buck converter (down-step from 12 V -> 5V)

 

[GJETSON]

That's really cool! Congrats. I have been wondering when our battery packs will have a small 12V module to power all the electronic systems.
Or maybe since we already have a crazy 400V -> 12V DC/DC converter, we can start to see 5V and 3.3V electronics natively supported rather than adding all that cost for each ECU module to have it's own buck converter (down-step from 12 V -> 5V)

Not even Tesla has done it yet. If it was easy to get rid of, they would have been the first to do it.

 

[jefro]

I have only seen one company that had a general auto drop in case in LiFePo4 and maybe they did have a heater too.

The reason I never installed one is the common ones don't have an easy way to hold them other than some makeshift over top clamp.

I do have some 12v batteries and not overly sure the claims on each product is what it might have in relation to a lead battery.

 

[Tag]

Any idea how these were "winterized?"

"The RB20-LT features the same size and performance as RELiON's RB100, but can safely charge at temperatures that drop below 0°C (32°F) using a standard charger. The system features proprietary technology which draws power from the charger itself, requiring no additional components. The entire process of heating and charging is completely seamless for the user. Simply plug the battery into the regular lithium charger and the internal heating and monitoring system takes care of the rest. Because it takes time to heat the cells, the charging process will take a little longer in below freezing temperatures."

The reason I never installed one is the common ones don't have an easy way to hold them other than some makeshift over top clamp.

Thankfully I have access to a 3D printer and was able to create a platform to bring the battery up to the top bracket with room for foam to dampen vibration.

 

[jefro]

My bracket is at the bottom like many cars where a sort of wedge grips a spot on battery sides.

 

[LarryO]

"The RB20-LT features the same size and performance as RELiON's RB100, but can safely charge at temperatures that drop below 0°C (32°F) using a standard charger. The system features proprietary technology which draws power from the charger itself, requiring no additional components. The entire process of heating and charging is completely seamless for the user. Simply plug the battery into the regular lithium charger and the internal heating and monitoring system takes care of the rest. Because it takes time to heat the cells, the charging process will take a little longer in below freezing temperatures.


Thankfully I have access to a 3D printer and was able to create a platform to bring the battery up to the top bracket with room for foam to dampen vibration.

The issue with this scheme is that there is no separate charger to plug into the battery. This type of battery has 3 terminals and not 2 like the Bolt.

 

[LithiumMoto]

Sounds like the BMS couldnt handle the load. You need to ask about the BMS capabilites on any lithium battery, Unfortunately, Buying a lithium battery nowadays is like getting a box of chocolates...
its not the Ah that determines the dicharge rate.