Under bonnet lithium. My experience

The battery was warranted for under bonnet.. as long as it was insulated.. I like to experiment..

did I blame the battery.. I was pretty sure I clearly said I didn't really know what caused it.. Did you fully understand the commentary? please rewatch..

Well yes you did blame the battery as you said it failed when it got hot. You may have added "I didn't really know what caused it" but again you did say it failed on the last trip during elevated temperatures. Anyone reading the review would walk away thinking don't put a Lithium batteries under bonnet as there not going to be able to handle it. In the case of the battery you selected it may well be a valid point with a temperature rating of 40C but it does not apply to all Lithium batteries, I have a DCS extreme under bonnet in a Prado and have not had any issues with it including hot conditions to date, I selected that battery as it has a working temperature rating of -25 degrees to 85 degrees C and can handle a winch.

The direction to insulate the battery is interesting, insulation only slows the transfer of heat ie an esky is insulated but your not going to store your cold beer in it thinking it will remain cold without adding ice! insulation it is not active cooling, put a battery in a 60C environment wrapped in a thin layer of styro foam and it will within a not to long period heat up to that temperature. The other aspect is the cells generate heat as the charge, the cell balancers also generate heat and if you look at the BMS they are usually mounted on large heat sink to disperse the heat they generate. Being directed to insulate the battery is interesting as the battery case only contains a small amount of free air and once heated how do you shed the heat through an insulated case?

From memory though you indicated the maximum heat your noted was 40C, which in the world of electronics is very low and one would not expect the electronics to be having issues at that temperature, possibly the battery charging side is set to shut down at temperatures above 40C but again is very low for it to be an issue for the electronics or the cells for that matter one would normally expect it to be in the range of -20 - 60C.

Bit harsh Leigh. The specs for cheaper LFPs tell part of the story about their limitations (temp, discharge rates etc) but experiences like JJs are useful to learn, even if we don't know the actual cause of the failure. I suspect if the seller pulled the battery apart the answer would have been pretty clear. The reason it stopped charging at hiugh temps is almost certainly clear - the BMS (and sensors) did the job.

A very quick look at some battery operating temp specs for some common 12V LFPs (~100Ah) :

$
VoltX
Prismatic
Working Temperature Range: Charge: 0°C to 45°C; Discharge: -20°C to 50°C

$
Giant
Prismatic
Discharge : -15 ~ 50oC ; Charge : 0 ~ 40oC

$
Atlas (from same seller)
Pouch
Mentions up to 60 degrees but no specs?

$+
Solar King
Cylindrical
Operating Temperature Range: -20°C ~ +60°C

$+
Duramax
Prismatic
Operating Tempuratures: Charging = 0C ~ 45C | Discharging = -10C ~ 60C

$+
Itechworld
??? cell type
Optimal charge temp range: 0°c to + 45°c; Optimal discharge temp range: -20°c to + 60°c

$$
Enerdrive eLITE
Prismatic
Battery Charge Temperature 0 ? 45°C; Discharge Temperature -20 ? 60°C

$$$
Revolution
Pouch
Optimum: -10 ~50ºC | Operational: -40 ~ 80 ºC

$$
DCS
Cylindrical
-30 to +80 degrees C

Yes and...

The battery selected has a charge rating of 40C, as everyone knows the ambient temperature in summer in Australia can exceed 40C in the shade. Now I can understand people experimenting with different setups but mounting a battery that can only handle 40C under bonnet then going north is my idea of destructive testing. It's not a matter of will you have problems but rather when.

Honestly I can't see why anyone would put a battery rated at 40C in the engine bay of a car even if the seller indicated it will be fine just wrap it in a bit of insulation! The outcome wasn't a surprise, the surprising aspect was that the battery lasted as long as it did. So hopefully the video will warn others not to try it with the same battery.

Now the the OP has moved it to the rear of the vehicle hoping all will be well, it may work but lets look at it logically. Is it possible for the inside of a car to exceed 40C when parked in the sun, yep it sure can. Figures such as 30C or more hotter or twice the ambient temperature are quoted. So if the ambient is 40C the internal temperature of the car could be up around 80C. Would it be a good idea to install a battery rated at 40C into the back of a car I personally I don't believe so if you want reliability. Would it be a good idea to charge the battery via solar panels for instance when the cars parked up in the sun I suspect not.

I would not be surprised if you see series two of this video down the track with the same red warning circle with a slash through it regarding installing the battery in the back of the car.

Probably correct Allan but it does raise the question as to how the under-bonnet rated LFPs deal with both the external and internal heat.

DCS seems to have some credibility in the LFP field. Here's an interesting article he wrote on an under bonnet setup:

Dual DCS LFP Setup

I had to insulated it as i did to be able to claim any warranty.. I understand the heat physics. I don't disagree that the battery also generates heat.. but its what I was asked to do to claim any warranty..

Hi Pete,

I could be wrong, but are you sure the Lithium battery in you EBike is Lithium Iron Phosphate, or is it Lithium Ion? Two different chemical compositions, that react differently when being charged.

Macca.

Was years ago, but most likely same as battery below, so most likely L-Ion. Replacement 13 amps but most likely L-Ion as well.

https://www.ebay.com/p/24029950238

Yep, Li ions (in phones, laptops etc) deteriorate pretty quickly if kept constantly on charge - very easy to do on a laptop. Most 12V LFPs should manage overcharging via the BMS but better to be safe than sorry and disconnect if you're storing your LFP (which are slow to discharge with no load anyway)

The brand is written on the battery!

But I couldn't read it! Or at least I couldn't when I wrote that. But on a larger screen and in full HD I now can. The point remains that he used a brand that wasn't one of those that claim to be suitable for under bonnet.

They claim a 5 year warranty under bonnet.. all lithium cells are basically the same.. so the under bonnet claim comes down to the BMS and heatsincing, but mainly just the risk the company is willing to take..

I couldn't see this statement on their website and I just had another look and I still can't. They do claim that this brand of Lithium is ok at higher temps, which could imply under-bonnet is fine, but I couldn't locate that specific statement. I'll take your word for it, but it's odd that they don't publicise it more prominently.

What I did find was a statement that putting an _AGM_ under-bonnet voids the warranty, which seems odd, as isn't that where most of them go?

All lithium cells aren't basically the same type, or quality, JJ. Some 12V Solar King LFPs changed from prismatic to cylindrical while I was researching and shopping around a while back, some use pouch cells (Renogy did at one point, may still do). Been a while since I researched but from memory cylindrical cells are better for dissipating heat. Love your work btw.

I mentioned DCS ($$$) elsewhere. Just found this video which might be of interest. This fella will be familiar to many forumites. Talks about temps and cylindrical cells, among other things:

DCS LFP Review

If you read the fine print, DCS shorten their warranty from 4 years to 3 for under-bonnet use.

Just to add a little more, Allan's point that elevated temperature shortens life was one that I put to my auto-electrician when he was installing my DCS. How _much_ does putting it under the bonnet shorten the life of the battery? The answer I got was that no-one knows at this stage, because it's all a bit new. In that sense putting a DCS under the bonnet was a bit of a gamble. The 25% shorter warranty is probably just a cautious guess by DCS.

You'd like it to last long enough to compensate for the far higher cost compared to AGM. But there are enough DCS batteries running around under enough bonnets to give me some confidence that I won't have the OP's experience. My auto-electrician has a pair of them under his bonnet, so he has a vested interest in ensuring that they have a respectable life.

Lithium don't like heat it seems, the first time I heard this was many years ago when supposedly an early adopter in the USA claimed his Lithium batteries stored in a side locker had shown a loss of capacity and he put this down to the locker getting hot from the sun shining on it. Since then we now have float charging shortens life, leaving them in a high state of charge shortens life etc.

I have seen papers suggesting the reason why floating and leaving them charged shortens their life but nothing from the industry as a whole stating the reasons, I haven't seen any definitive lab results that have been duplicated by others independent labs etc.

Personally my Lithiums are floated, they are cycled daily when in use from fully charged to whatever each day. They live in an outside locker on the camper and it is heated from the sun. When stored I lower down to around 50%SOC. Had them a few years now and still test to their rated capacity.

I also have a DCS unit under bonnet, interestingly with the car mobile I haven't seen the battery hotter than 10C above the ambient except when the car stopped and heat builds up under the bonnet, this I would image would be a similar rise to the batteries in the locker when the sun is shining on the side of the van, possibly hotter.

Do I think the life of the under bonnet will be shorter, well given Lithiums only have a finite amount of electrolyte, a lot less than your lead acid then one would suspect so. Also charging them at a rate where they will gas and vent is probably not a good idea. In my case I charge the under bonnet battery directly off the alternator, so when it is low there is a olt of current flowing but once the battery approaches near full it tapers off quickly. The max charge voltage it sees is around 14.2V on a cold day and lower on a hot so the battery is never pushed to a full charged when cycling daily so gassing is not likely to occur. Charging with a DCDC charger though might be different, it will charge to 14.4V or higher and fully charge it then maintain that for whatever time it set for before dropping to float. The fully charged battery will then sit there floating charging for whatever period, so fully charging under bonnet Lithiums might not be a good idea.

My under bonnet battery is three years old now and still tests at the same capacity as new so will it age quicker, good question, it does get subjected to heat soak when the engine is turned off until the engine cools down, but then the batteries in the van locker can be in the sun all day long for days on end, guess time will tell.

Correct.. these cpmp[anies claiming this, are just using good components and taking the risk.. the cells are nearly all the same across all batteries.. There are only a few places these cells are made, and they are all of the same chemistry.. Its mainly use good components in the BMS, and have a good marketing department..