Strange Lithium & Victron Controller Voltage Readings

[Purnong]

I have a 120ah lithium battery with a 100/20 Victron solar controller and 250w solar panel, the battery is a commecially bought drop in
The victron will sometimes report a low voltage overnight of 11 volts or so, most times it says 13.16
I have a seperate battery monitor that shows the battery over 13 volts overnight, this one logs a reading every 2 minutes while the victron only gives the highest and lowest values
When I first got this battery it would randomly cut out for a second, the fridge and radio would turn off, at that time I had an epever controller and apparently they can do strange things with lithium batteries so I changed it to the victron
Since having the victron I've had no more battery cutting out but I am seeing these strange voltage readings
The battery is running a 38 litre Engel as a fridge and a 45 litre Oztrail as a freezer overnight and seems to be working fine, it gets down to 92-94% most mornings and is usually fully charged by midday
I'm wondering if there is some wierd switching thing with the victron mppt doing this or if it is a fault with the battery, bearing in mind the other battery monitor shows perfect readings
It has me stumped, Anyone like to offer any advice with this, I'm happy to supply the spreadsheet readings from both devices if that would be useful

 

[HRTKD]

Is there an inverter involved? Or are the refrigerator and freezer run off of DC?

I suspect that the refrigerator and/or freezer are kicking off and overdrawing the battery for a very short period of time. Do the refrigerator and freezer have a defrost feature?

 

[Purnong]

Is there an inverter involved? Or are the refrigerator and freezer run off of DC?

I suspect that the refrigerator and/or freezer are kicking off and overdrawing the battery for a very short period of time. Do the refrigerator and freezer have a defrost feature?

No inverter involved, I probably should have mentioned that this is all 12 volt
With both fridges running they draw around 7 amps and no defrost function

 

[HRTKD]

Is it possible that both the refrigerator and freezer turned on at the same time? A motor will require more startup amps than running amps.

If you turn off power to both the refrigerator and freezer, allowing them to come up in temperature, then turn power back on to both at the same time, it's possible you could cause the low voltage situation.

 

[Purnong]

Thanks for the replies HRTKD I understand what you're saying but it's hard to see that drawing the battery to such a low voltage
What gets me is the difference in the readings between the two devices
I'd tend to trust the Victron over the other which makes me think something strange is happening with the switching in the mppt

 

[HRTKD]

Check all your connections. Many of the voltage issues seen on the forum are due to bad connections.

 

[timselectric]

Bad connections equals heat, and heat is the enemy.

 

[Purnong]

Thanks again for the replies
I have been over the connections and can't find anything wrong, I'll go over them again
I might plug the fridges in to the house power for a few days and see if that stops it happening
The Bluetooth monitor is installed direct to the battery terminals as are the fridges so if something strange was happening in the battery it should pick it up
Nothing is installed on the load terminals on the controller
I'll have to dig a bit deeper into all the connections again