I’m pretty sure it’s normal but want to verify.
Currently my battery is showing a min cell temp of 40.3°F and a max cell temp of 41.0°F. The ambient temp just outside the battery is 34.5°F. The temps have been stable and within a degree for hours.
The amp draw is only 0.4A, so I’m surprised there is that much heat being generated.
Battery is a Victron Lithium NG 25.6-300.
Seem normal? Sure will help with winter battery heating requirements.
This can also be due to the difference in calibration of the temperature sensors.
Your difference is <6F, or ~3C. Analogue temperature sensors can be typically +/-2C (3.6F), so this may well be within error limits. (2 sensors so 2x error).
Whilst the battery temperature appears stable, it will have a very high thermal mass, so temperatures are likely to take many hours to stabilise. Also, this depends on the positioning of the sensors.
Adding to Mike’s points above, it also depends on what the battery is sat on as conduction is more effective at heat transfer than convection from the air, especially if the air is not moving. My NG batteries sit on the boats baseplate below water level, which moderates the battery temperature so they are nearly always different to the air temperature inside the battery box.
Thanks, that’s what I figured.
The ambient air temp sensor is on the side of the multiplus-II and is the unused Victron sensor with the readout thru my Cerbo GX. I’m not sure if I can calibrate anything or not.
The last thing I want is for the batteries to be reading low and trying to charge when they shouldn’t.
The charge / no charge decision will be based on the BMS battery temp, rather than the ambient.
Temp calibration is not possible with the GX / Venus software.
Temperature readings are also affected to a degree by the length of the thermistor cable.
Yes, I’m aware the BMS will make the charge/no-charge decision. I was just making sure the warmer battery temp was normal and not reading warmer than the battery actually is for whatever reason.
Be aware that technically, ambient temp is different from air temp though I understand what you mean. Ambient temp means the temp around a piece of equipment, which is often different from air temp. Your “ambient air” temp depends on where the sensor is mounted. My experience is that you can’t really depend on temp sensors, unless they are properly calibrated.
I don’t think you need to worry. The slightly warmer temp is normal, My batteries will run about 2C warmer than ambient - House not utility room. Better than lead where the batteries were running about 15C warmer than ambient.