Long-term battery test - one week of cold beer

Wueste · Aug 5, 2023

Hello friends,

There are so many theories about the double battery system.
I tested it once. The Grenadier was parked for a week.

Last Sunday I parked the car and switched on the fridge in the trunk.
Every day of the week I checked whether the beer was still cold.

Monday 67% - cold beer

Tuesday - alcohol-free day

Wednesday 50% - cold beer

Thursday 25% - cold beer

Friday 13% - cold beer

Saturday 1% - warm beer

The power switch was without light - so all off.

Waited until 0% - started the car - no problems, started immediately.

Short trip to the G-Class in the garage yard, after 2 km drive it was already 12% again.

Drove another 20 minutes, then home and took a cold beer from the fridge.

Now I connected the charger.

That was now better than I would have expected.
The car is a petrol engine and the fridge is a Waeco CCF35, about 20 years old.
I'll answer questions about the beer in the beer thread. #

greetings wueste

Jean Mercier · Aug 5, 2023

Wueste said:
Hello friends,

There are so many theories about the double battery system.
I tested it once. The Grenadier was parked for a week.

Last Sunday I parked the car and switched on the fridge in the trunk.
Every day of the week I checked whether the beer was still cold.

Monday 67% - cold beer
View attachment 7822452
Tuesday - alcohol-free day

Wednesday 50% - cold beer
View attachment 7822453
Thursday 25% - cold beer
View attachment 7822454
Friday 13% - cold beer
View attachment 7822455
Saturday 1% - warm beer
View attachment 7822456
The power switch was without light - so all off.
View attachment 7822457
Waited until 0% - started the car - no problems, started immediately.
View attachment 7822458
Short trip to the G-Class in the garage yard, after 2 km drive it was already 12% again.
View attachment 7822459
Drove another 20 minutes, then home and took a cold beer from the fridge.
View attachment 7822460
Now I connected the charger.

That was now better than I would have expected.
The car is a petrol engine and the fridge is a Waeco CCF35, about 20 years old.
I'll answer questions about the beer in the beer thread. #

greetings wueste

With 0%

left, you'd better not drive

das mo · Aug 5, 2023

Wueste said:
Hello friends,

There are so many theories about the double battery system.
I tested it once. The Grenadier was parked for a week.

Last Sunday I parked the car and switched on the fridge in the trunk.
Every day of the week I checked whether the beer was still cold.

Monday 67% - cold beer
View attachment 7822452
Tuesday - alcohol-free day

Wednesday 50% - cold beer
View attachment 7822453
Thursday 25% - cold beer
View attachment 7822454
Friday 13% - cold beer
View attachment 7822455
Saturday 1% - warm beer
View attachment 7822456
The power switch was without light - so all off.
View attachment 7822457
Waited until 0% - started the car - no problems, started immediately.
View attachment 7822458
Short trip to the G-Class in the garage yard, after 2 km drive it was already 12% again.
View attachment 7822459
Drove another 20 minutes, then home and took a cold beer from the fridge.
View attachment 7822460
Now I connected the charger.

That was now better than I would have expected.
The car is a petrol engine and the fridge is a Waeco CCF35, about 20 years old.
I'll answer questions about the beer in the beer thread. #

greetings wueste

Where did you connect the fridge? Plug-wise. As I recently got stuck with battery at 50% just before all system went black.

Wueste · Aug 5, 2023

das mo said:
Where did yoy connect the fridge? Plug-wise? As I recently got stuck with battery at 50% just before all system went black.

The frigde was connected in the trunk via the standard socket.

Scan4 · Aug 5, 2023

Thats how Sciencefictionfilm is explained….

bakepl · Aug 5, 2023

Wueste said:
The frigde was connected in the trunk via the standard socket.

Thank you for this test, much appreciated. I'm thinking 10.9v might just start a petrol engine so unsure if the smartpass feature of the auxiliary battery assisted it to start or not - unless you saw a fault being shown on the smartpass device indicating the start assist feature has been used. I'm not confident however this is the best scenario i.e. draining down the starter battery so deep rather than draining the auxiliary battery first - I'll be wiring mine via the smartpass as it will stop discharging via the consumer outlet at 11.5v and protect the battery from that deep discharge. On a side note the CCF35 is similar to my CF35 and I can also adjust the low volt cut off to either 10.1, 11.4 or 11.8v.

Asnes · Aug 5, 2023

You will permanently reduce the amp hour capacity of a lead acid battery (AGM or otherwise) running it down below 50% state of charge fyi. The lead plates will become sulfated. Lithium is fine to 20% before BMS turns them off to avoid irreversible damage but lead acid is a different story.

Rule of thumb don’t let that battery go below 12.2v if you want to maximize lifespan and performance.

Wueste · Aug 5, 2023

Asnes said:
You will permanently reduce the amp hour capacity of a lead acid battery (AGM or otherwise) running it down below 50% state of charge fyi. The lead plates will become sulfated. Lithium is fine to 20% before BMS turns them off to avoid irreversible damage but lead acid is a different story.

Rule of thumb don’t let that battery go below 12.2v if you want to maximize lifespan and performance.

We all have to make sacrifices for science.

AnD3rew · Aug 6, 2023

Asnes said:
You will permanently reduce the amp hour capacity of a lead acid battery (AGM or otherwise) running it down below 50% state of charge fyi. The lead plates will become sulfated. Lithium is fine to 20% before BMS turns them off to avoid irreversible damage but lead acid is a different story.

Rule of thumb don’t let that battery go below 12.2v if you want to maximize lifespan and performance.

Yes was going to say, batteries really don’t like getting that low. Definitely shouldn’t make a habit of it

Deichrutscher · Aug 6, 2023

A little notice:
The undervoltage protection of the refrigerator measures at the end of the connecting cable.
Even when the battery is fully charged, less voltage can arrive at the refrigerator than measured directly at the battery.
This can mean that the battery still has 12.3V, but the undervoltage protection on the refrigerator is already switching off.

With my pickup, the cable length from the battery to the refrigerator was over 5m (8mm²/ AWG8). When the fridge turns on the compressor, it draws about 5-6Amps.
The 5m cable (including the fuses and plugs) then dropped 0.7V. The undervoltage protection then responded even at the medium setting.

This situation is also known to some who connect the freezer to the cigarette lighter in the car, where the plug tends to get hot.
I then laid thicker cables (16mm²/ AWG5) and connected the connection cable directly without the cigarette lighter plug.
That was the solution for me, the undervoltage protection no longer responds too early.

emax · Aug 6, 2023

Asnes said:
The lead plates will become sulfated.

Although you are correct with the DOD numbers, the sulfation only occurs (to my knowledge) if the high DOD (low voltage) lasts for a while. If recharged swiftly there shouldn't be much of a loss - if at all.

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Long-term battery test - one week of cold beer

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