Hello, I have 3x 130Ah Agm Victron deep cycle batteries connected in parallel (12V) that are being charged by Victron Phoenix Smart IP43 Charger. I also have Victron Smartshunt with corresponding temperature sensor connected with VE.Smart networking to IP43 charger and all devices are connecte to Ekrano GX with VE direct cables. I have the expert mode enabled on the IP43 settings, absorbtion voltage is set to 14.40V and temperature compensation is set to -24.00mV/C as recommended by Victron for this type of batteries. Today battery temperature was 17 celsius and absorbtion voltage was around 14.60V (which coincides with temp compensation settings). My concern is the following; will the charging voltage be increasing in parallel to the temperature decrease without any top limit? If yes then at 5 celcius temperature, absorbtion voltage would be around 14.90V. Would that be harmful or ok for the batteries on a long term? Thanks
Hi @Elh
Pb batteries are very sluggish when cold, and need that extra V to charge at a similar rate to when specced at 25degC. But there’s limits that will be adhered to when applying the correction. The manual for your particular unit should state those, perhaps 6 to 50 degrees. If actually outside that then maybe you could consider deferring charging?
But normally it won’t hurt at all, providing the Temp is being passed across and applied correctly.
Hi @JohnC,
Above a certain temperature the temperature compensation will decrease the configured voltage and below it will increase it. But what temperature is this? I couldn’t find it in the Victron documentation. I have a Phoenix Smart IP43 charger (12/50/3).
Thanks,
Pierre
Hi @PierreV
For lead batteries, the theory says that no correction is needed between 50°F (10°C) and 86°F (30°C)
If the average battery temperature exceeds 86°F, the float charge voltage shall be reduced by (AT - 86) x .003Vpc (but not less than 2.18Vpc).
If the average battery temperature is lower than 50˚F, the float voltage shall be increased by (50 - AT) x .003Vpc.
Vpc = Volts per cell.
AT = the average operating temperature.
Hi Pierre,
It’s 25 degC that Victron use, which is pretty much the standard.
And it starts working straight away when deviating from that, which is what you want with Absorption level V settings.
Hi John,
Thanks! This explains what I see. I first thought that my charger was broken because the absorption and float voltages were too high (higher than the configured values). Then I realised that the temperature compensation could be the reason for these higher voltages.
The float voltage was 14,06V instead of the configured 13,80V, hence a delta of 260mV. The temp compensation is configured as 16,2mV/C. So if the center temperature is 25C the 14,06V is to be expected when the temperature is 9C, which it was 
What a relief! This would have been the second charger that broke in a year (not a Victron).
@JohnC & @Alex Pescaru, many thanks for helping me out!
Cheers,
Pierre