Battery conundrum

[Martyn 4950]

Ok another battery question. Had new batteries in November 2019. Use the van as a daily vehicle and put on charge once a month.
Was in van last night for 2 hours with heater on no 2 setting and one interior light on. B
Battery went down to 60% very quickly
Checked battery this morning and was back up to 100% without any hook up. Had fridge on for about 2 hours and battery down to 90 % . Im completely baffled by this dark science

 

[ThomasHJ]

Did you notice the voltage by any chance? The % is said not to be very reliable. Sometimes it goes down, then comes back up again. Sometimes is says 60% at a certain voltage and then 60% at a different voltage. The voltage readings are more reliable. If you are worried enough, do some tests. I would recommend charging it on EHU and then turning on the fridge set to max. Then take pictures of the central control unit (voltage readings) every hour or so in the beginning and every 12 hours after that. That should give some decent information on which to determine if there's something wrong.

 

[Calimili]

I'm by no mean a battery expert, but you cannot read the charge state of your battery, derived by the Voltage when a load or a charge has been applied within the last 1-2 hours.
You need to wait until the cells within the batteries equalise themselves.

 

[ThomasHJ]

But you can measure the time it takes your batteries to discharge, which in the end is what counts. Because what you want to know is whether or not something is wrong. Whether or not your batteries are discharging in a normal speed or too fast. If it turns out teh batteries discharge faster then normal, that would be an indicator to check the batteries themselves.

 

[Calimili]

But you can measure the time it takes your batteries to discharge, which in the end is what counts. Because what you want to know is whether or not something is wrong. Whether or not your batteries are discharging in a normal speed or too fast. If it turns out teh batteries discharge faster then normal, that would be an indicator to check the batteries themselves.

yep, but in practice not easy to do accurately as loads change. Lights on/off, fridge' compressor kicks in intermittently and depending on temperature, same for the diesel heather. The Diesel heather may make a big difference if it is always on and blowing hot air, or if it switches on and off as the piezo draws a lot of current.

 

[WelshGas]

Ok another battery question. Had new batteries in November 2019. Use the van as a daily vehicle and put on charge once a month.
Was in van last night for 2 hours with heater on no 2 setting and one interior light on. B
Battery went down to 60% very quickly
Checked battery this morning and was back up to 100% without any hook up. Had fridge on for about 2 hours and battery down to 90 % . Im completely baffled by this dark science

As has been said the % shown is just a calculation based on the present current draw and more of a gimmick . The voltage is more important and more accurate. The Parking Heater takes a large current to start up, for the glow plug ignition system. Once fired up it takes very little current to continue. Likewise the fridge. The compressor runs a lot until down to temperature then very little thereafter.
It is more important to note the voltage which is less accurate when heater or fridge is starting up and more accurate when running and even more accurate 30 mins or so after everything is off.
The fridge and heater will automatically switch off at about 11.5 v and remember you can only use about half the capacity of the battery system without damaging the batteries. On this diagram 0% is of the usable capacity rather than the total capacity, to avoid permanent damage.

This is a handy memoir.

 

[ThomasHJ]

So @WelshGas if I understand correctly, you should never let the batteries get below 11.75V? Because after that it could be damaging to the batteries?

 

[WelshGas]

So @WelshGas if I understand correctly, you should never let the batteries get below 11.75V? Because after that it could be damaging to the batteries?

You should try to avoid that. It does depend how long they are at a low voltage. Doesn’t matter that much if you are going to be starting the engine or plugging into EHU in the next few hours.
If the fridge or heater shuts down because the voltage shows 11.5v, once shut down the voltage would probably rise above that level, as the voltage is lower when the battery is being used rather than at rest.

 

[Martyn 4950]

As has been said the % shown is just a calculation based on the present current draw and more of a gimmick . The voltage is more important and more accurate. The Parking Heater takes a large current to start up, for the glow plug ignition system. Once fired up it takes very little current to continue. Likewise the fridge. The compressor runs a lot until down to temperature then very little thereafter.
It is more important to note the voltage which is less accurate when heater or fridge is starting up and more accurate when running and even more accurate 30 mins or so after everything is off.
The fridge and heater will automatically switch off at about 11.5 v and remember you can only use about half the capacity of the battery system without damaging the batteries. On this diagram 0% is of the usable capacity rather than the total capacity, to avoid permanent damage.

This is a handy memoir.

View attachment 68005

Thanks for that.....so could you do a little experiment to see if all is ok ? Any suggestions....sorry for sounding thick

 

[ThomasHJ]

I also use the van as my daily driver and charge it for 12 or sometimes 24 hours roughly every month. When i recently seemed to have a problem with my batteries, I did a test as mentioned in my post above. This at least will tell you if your batteries allow you to 'camp' without EHU for the 'normal' amount of days. 'Normal' being the average amount of days that people here on the forum say that they can go without EHU (3-4 days sometimes even more). In my case it turned out my completely new batteries wouldn't even last me 48 hours. That was a clear sign of something being wrong. So i'd try to mimic a somewhat realistic camping experience/usage during camping. That will give you a general idea of whether your batteries are fine and it's just a case of the readings being a bit weird (which is normal) or if you've got a problem.

 

[DanFog]

I also use the van as my daily driver and charge it for 12 or sometimes 24 hours roughly every month. When i recently seemed to have a problem with my batteries, I did a test as mentioned in my post above. This at least will tell you if your batteries allow you to 'camp' without EHU for the 'normal' amount of days. 'Normal' being the average amount of days that people here on the forum say that they can go without EHU (3-4 days sometimes even more). In my case it turned out my completely new batteries wouldn't even last me 48 hours. That was a clear sign of something being wrong. So i'd try to mimic a somewhat realistic camping experience/usage during camping. That will give you a general idea of whether your batteries are fine and it's just a case of the readings being a bit weird (which is normal) or if you've got a problem.

Can you tell what your problem was? I have 2 new batteries, and I also can't camp for 48 hours with heater running. The heater is running on 5 in the evening and 2 over night.

 

[ThomasHJ]

Can you tell what your problem was? I have 2 new batteries, and I also can't camp for 48 hours with heater running. The heater is running on 5 in the evening and 2 over night.

Sure, there's a post about it here. It could be many different things, but in my case it turned out to be the earth shunt under the fridge being broken, causing the readings on my central control panel to be wrong, when in reality my leisure batteries were just fine and not discharging as fast as the control panel was telling me.