Flipping the usual dual battery system, lithium as starter battery, with small AGM backup.

[roving1]

I have a theory of a way to go that I don't think I have seen much of.

I'm thinking of going to a system with a 100ah lithium as the starter house battery in OEM location with a very small racing type AGM stuck somewhere else under the hood isolated as a backup battery.

Benefits:
I don't really want to parse circuits out with what is OEM and what is for the house battery. Seems like a waste of time. No standalone bms needed. With my modest needs for power this would probably also mean I don't have to mess with solar. Fast charging for LI suits my normal use case and I am OK with idling I bit to extend boon docking. System would probably never run out of power for me and if I did it would be quick to top off and then AGM would be the safety net for starting.

Issues:
I don't really know how LI battery charges in cold. I know the internal BMS won't let it charge but what I don't have a sense of is what happens in normal use. Does loading it up heat it enough to charge?What about driving around? Need a battery blanket in extreme cold? I don't really know.

This is going into a 1st gen Tacoma with a 2.7 which is about the best case scenario for not bad underhood temps so I am not really worried about heat killing the battery. Also the weight savings and open bed nature of this truck don't really lend itself to normal dual batteries or house battery in the bed.

So why is this a good or stupid idea in everyone's opinion?

Even if I don't go the lithium route I think I will still go the starter/house as the same battery with a small battery backup.

 

[luthj]

Lithium batteries cannot be charged below a certain temperature, usually around 35F. For your application I would suggest leaving the AGM battery permanently in parallel with the lithium battery. It would be a small parasitic draw from the lead battery on the order of 50 to 200 mA. For cold-weather operation you need to install some type of heating pad on the lithium battery. In this type of situation you would start the vehicle and engage the heater pad. once the lithium battery is up to temperature it will connect and start charging. The other important part about leaving the lead battery permanently paralleled, is that these lithium batteries can suddenly disconnect internally. This can be due to high or low temperature or cell in balance. Having this occur on a running vehicle with an alternator and no second battery connected can result in dangerous voltage spikes which would damage the vehicle. Leaving the lead battery connected provides protection against this type of event.

Also not all lithium batteries are suitable for starting applications. The solid-state internal relay on many cannot handle surge currents of 200 to 500 A required to start big engines. So be very careful with your selection.

 

[vintageracer]

In reading your reply and personally knowing little at all about lithium batteries you state that lithium batteries cannot be charged below 35 degrees therefore my question:

How do you charge lithium batteries in cold temperatures (35 Degree's or less) in such vehicles as a Tesla or Nissan Leaf?

 

[luthj]

In reading your reply and personally knowing little at all about lithium batteries you state that lithium batteries cannot be charged below 35 degrees therefore my question:

How do you charge lithium batteries in cold temperatures (35 Degree's or less) in such vehicles as a Tesla or Nissan Leaf?

Battery temp is usually well above ambient in cool weather, as the large packs have decent thermal mass. Tesla (and all other EV MFGs) use a battery thermal management system. In the tesla the pack has cooling/heating lines run through it. The coolant is heated or cooled as needed to keep the batteries optimal.

Since lithium packs can discharge without issue below 35F, the issue is only with charging. So if you plug in a pack thats too cold, it will heat itself up until its ready to charge. Usually if the bank has been used a significant amount, it will be warmed up to normal operating temp range.

 

[SanJuan]

Have you looked at Relion's "LT" (low temp) LiFePO4 100ah battery?

 

[luthj]

Have you looked at Relion's "LT" (low temp) LiFePO4 100ah battery?

Those batteries use an integral heater, which is cool.

A battery can be equipped with a heater, and assuming the BMS is decent, you can heat until it reconnects.

 

[Deleted member 9101]

I have a lithium battery on my motorcycle. It hands down starts it better than any other battery style that I have tried.

 

[DCH109]

I am not sure why you would want to do this. From my understanding and I am very rusty on my understanding. The battery has 2 main functions.

1. to start the car
2. as a buffer for when the electrical system (alt) cannot provide enough power to the system and then the battery is used as needed. I.E accessories like winches, high power lights, fridge etc.

 

[Alloy]

Charging Lithium below 35F degrade the plates......"like" FLA (flooded lead acid) left sitting at 11 volts.

It takes hours to (imagine thawing a block of ice) raise the core temperature of a Lithium battery with a battery warmer.

The Relion battery 12V heating uses a few amp hours to heat the battery. For daily use it is better to keep the battery bank in heated space.

 

[john61ct]

If you have a big enough House / Accessories bank, no harm in using that for cranking, better use of limited space than a dedicated Starter.

For redundancy can carry a lithium jumpstarter sized for diesels, or

keep one battery out of the bank isolated from draining too low via an LVD.

 

[roving1]

Lithium batteries cannot be charged below a certain temperature, usually around 35F. For your application I would suggest leaving the AGM battery permanently in parallel with the lithium battery. It would be a small parasitic draw from the lead battery on the order of 50 to 200 mA. For cold-weather operation you need to install some type of heating pad on the lithium battery. In this type of situation you would start the vehicle and engage the heater pad. once the lithium battery is up to temperature it will connect and start charging. The other important part about leaving the lead battery permanently paralleled, is that these lithium batteries can suddenly disconnect internally. This can be due to high or low temperature or cell in balance. Having this occur on a running vehicle with an alternator and no second battery connected can result in dangerous voltage spikes which would damage the vehicle. Leaving the lead battery connected provides protection against this type of event.

Also not all lithium batteries are suitable for starting applications. The solid-state internal relay on many cannot handle surge currents of 200 to 500 A required to start big engines. So be very careful with your selection.

Thanks this confirms some of the things I was thinking.

The way I was intending to use was in parallel with the engine running.

Thanks

 

[roving1]

Have you looked at Relion's "LT" (low temp) LiFePO4 100ah battery?

I have added to the list! I knew there was something that had this capability but I had long ago forgot which brand.
Thanks

 

[Stephan07]

I’m on my second Tesla...previous was a model S P90D. Now a model X P100D. I live in Boston but drive to upstate NY and Burlington VT a lot. 100% the battery had a hard time charging below 30 degrees.

I got stuck in Burlington last winter. Above 50F, with 20% charge left i charge at roughly 300+ miles per hour of charge. Well, it was 10 below. Car had been outside all day. It charged at 10 miles per hour. After 4 hours I had enough charge to drive to the next charger, and by the time the batttery eas warm enough.

I take my 4 Runner these days anytime it’s below 30. Inlso built. Portable lithium generator w 2 battle born batteries. Can be charged from AC/DC/ or the sun.

 

[john61ct]

Please don't propagate the fraudulent marketeer use of "generator" for portable battery powerpak.

If they include panels, then "solar generator", maybe.

 

[roving1]

Well while still in Mexico my normal OEM battery was really cranking slow in cold mornings. Before you laugh I'm in Toluca at almost 9K feet. Morning are often 25-27F out. Soooo I went and bought a decent AGM for starting duties. So since I was sort of forced to go this route I will probably go with a more traditional dual battery set up down the road.

Incidentally LTH is a pretty good battery brand in Mexico. They have stand alone stores and are sold at auto parts places. The parent Co is Johnson Controls, the people that make óptimas.

I know so many people that have issues with óptimas though I could not bring myself to pull the trigger. I was able to find a non optima AGM with as good or better specs as the óptimas under the LTH brand with normal non spiral construction and just a little more than half the cost of an optimas.