Ventilation / cooling for 150 Diesel auxiliary battery - Mod ideas?

[Daniel150 Member Find all posts View Profile Close Daniel150]

Glad you have a decent panel. That will help a lot. Sorry my calcs where based on the usual setups I see when people are having problems with their batteries.
I still feel your battery problems are related to being discharged too deeply due to being too small, not heat related.
Personally I’d avoid running a hybrid battery as a start battery though. It will have a shorter than necessary lifespan.
What fridge are you running to get those amp readings? I’ve tested most fridges on the market and they never come near that. Most are running a db35 or 50 compressor or something similar in size. I ask that question as I’m actually interested, not trying to be a smart a**e!

[GeeWhizz Senior Member Find all posts View Profile Close GeeWhizz]

55ah is too small for an aux battery. I wouldn’t even bother with one under 100ah.
You could try putting an amp meter on the fridge, I’d assume it’s going to draw 2-3 amps per hour.
Effective solar gain is gone by let’s say 6pm for example and effective gain returns at say 8am. That’s 14 hours at 2.5 amps. That’s 35amps over night.
Not sure on your solar panel, but let’s assume you are running a standard camping setup with a PWM charger. (Bcf, annaconda, supacentre). These will put in about 5-6 amps at full sun. Full sun from 8-6 is 10 hours or 50 amps. The fridge has taken 25 of these amps, leaving 25amps to charge the battery that has lost 35 amps. Follow???
Adding to that, it sounds like you are recharging lights and speakers etc off the solar as well which makes things worse.
The battery is then starting the next night already 10 amps or half the usable charge gone.

"Follow???" No way! Please use the proper terminology: Amps (A) and Amp Hours (Ah). Don't mix the two. Mixing your terms makes your analysis confusing at best and useless for beginners.

My Waeco CFX75DZ draws around 3.5 amps when the compressor is running - typically 20 minutes every hour. That's drawing around 1.2Ah every hour or 28Ah per day. Of course, the duty cycle is much higher in summer compared to winter: the current draw remains the same but the compressor spends more time running.

[Daniel150 Member Find all posts View Profile Close Daniel150]

Sorry for not using all the correct terminology… I will correct it for you. It was a basic analysis given to try and help out someone whose batteries are failing most likely from over discharge.
Maybe you have some relevant info on why his batteries are failing that you could contribute with?

My basic camping setups have always used about 50ah per 24 hours with a few led lights and a 12V fridge. That basically accounts for 2amps per hour on the fridge with real time usage over 24 hours. With correct charge cycles and a deep cycle battery, I usually get 3-4 years from an agm battery.

[Andy-150Diesel2010 Lurker Find all posts View Profile Close Andy-150Diesel2010]

Glad you have a decent panel. That will help a lot. Sorry my calcs where based on the usual setups I see when people are having problems with their batteries.

All good. We drifted a bit out of scope from the initial topic here so I hadn't posted the information. But for the record I have a 300W blanket, Victron 100/20 MPPT, as well as their "Smart Battery Sense" voltage and temperature monitor.

So the daily power generation side of things is well in order. Even in modest weather, overcast days etc. I'm still comfortably in front re: power generation vs comsumption.

I still feel your battery problems are related to being discharged too deeply due to being too small, not heat related.

No doubt that contributed to the first battery failure, but the second... Hmm. Either way, it was just too short a life for the battery for me to call them a good buy. My first 2 deep cycles were Century N70T, FYI.

I'm giving the Yellowtop a go for a change of brand, as much as anything else.

Personally I’d avoid running a hybrid battery as a start battery though. It will have a shorter than necessary lifespan.

I'm partly leaning towards moving the 55AH to the starter purely due to the age of my current starter. It's actually working perfectly fine still... no trouble turning over, but, it's at least 8 years old now. That's how long I've had it, plus however long the original owner had it before me. I think at least 3 years with him.

At the first sign of it getting sluggish, I could throw the Yellowtop 55AH in there as the new starter, and grab a new 66AH Yellowtop for the Aux.

How much worse could the hybrid be than my potentially 10+ year current starter? I think it's safe to say I've had my money's worth out of that one. Ha.

Kudos to Century though on their NS70X MF. Or my one at least, as it seems to be near immortal. Haha.

What fridge are you running to get those amp readings? I’ve tested most fridges on the market and they never come near that. Most are running a db35 or 50 compressor or something similar in size. I ask that question as I’m actually interested, not trying to be a smart a**e!

I'm running a Waeco CF40.

Published specs and all that aside though, it's all situational, right? Run the fridge and 4c vs 1c, run it on an 18c day vs a 40c day, full fridge vs an empty fridge, and on and on with the variables.. All completely different stories.

I usually go camping 9 months a year, outside of summer. Summer in the Melbourne high country sucks, I'll leave the 40c+ days for others to soak up, ha.

[Daniel150 Member Find all posts View Profile Close Daniel150]

All good. We drifted a bit out of scope from the initial topic here so I hadn't posted the information. But for the record I have a 300W blanket, Victron 100/20 MPPT, as well as their "Smart Battery Sense" voltage and temperature monitor.”

That’s awesome. Good to see people using a proper mppt and an appropriate panel size.


”How much worse could the hybrid be than my potentially 10+ year current starter? I think it's safe to say I've had my money's worth out of that one. Ha.”

Yep, that is pretty unreal for a start battery. The hybrid will do the job fine, it’s just in my experience they have a very short lifespan if used harshly.


Cheers, I have a 50L solely as a beer fridge. I run it at about 1 degree and yeah it draws a lot more than that. As I said my calcs where just a rough guide that I show people who seem to kill their batteries quickly

So to clarify, the first two that failed where proper deep cycles, or 55ah gold tops?? That’s really strange for a deep cycle to die that quick.

[GeeWhizz Senior Member Find all posts View Profile Close GeeWhizz]

A couple of points that I can offer. I think you're still using a wet cell aux battery. These are quite fragile when run down. As noted previously, at (around) 12.05 Volts the battery is considered to be at 50% of its capacity. Regularly discharging this type of battery below 50% is risky and will shorten its life.

Driving with a "flat" battery, particularly on rough roads, will shake the sulphated lead off the plates, resulting in sediment building up in the cells. Firstly, this will result in less lead on the plates (its pretty then anyway), meaning less energy stored. When the sediment build-up reaches the plates the battery will self-discharge, meaning end-of-life.

Generally, AGMs are not suitable as starter batteries because they can't deliver high starting currents. However, AGMs make a better choice for Aux batteries as their internal structure is more robust and able to take rough roads when discharged. Depending on the charger used on the Aux battery, its charging will be be delayed while the starter battery gets served first.

Finally, to get an accurate battery voltage reading, take the reading a couple of minutes after no charging or discharging occurring.

[Andy-150Diesel2010 Lurker Find all posts View Profile Close Andy-150Diesel2010]

So to clarify, the first two that failed where proper deep cycles, or 55ah gold tops?? That’s really strange for a deep cycle to die that quick.

The first 2 that failed were both Century N70T.

The new 55AH is a Yellowtop D34

[Daniel150 Member Find all posts View Profile Close Daniel150]

Ok, cheers I was misinterpreting that all along as you had two failed gold tops at 55ah. Hence why I was going down the line of over discharge given the sizing.
Hopefully the optima gives you a better run.