Can you charge AGM batteries below 32 F?
Yes, but for best battery life you really need a temperature compensated charger…
Everyone,
One of my writing colleagues just posted an article stating that charging AGM batteries at temps below 32 degrees F would damage them. So I posed this question to Fred Wehmeyer from U.S. Battery.
Dear Fred,
My understanding is that AGM batteries can be damaged by charging at high temperatures, but not low temperatures. I think my writing colleague is confusing AGM and Lithium battery charging at low temps. Can you offer any comments? -Mike
Dear Mike,
This is a common question regarding charging AGM batteries. The short answer is that it is acceptable if done properly. The long answer requires some explanation. When charging any battery, charging at very low temperatures (below 32°F) requires great care. 🥶
The best way is to use a charger with a temperature compensated charge algorithm. This requires a temperature probe from the charger to the battery so the charger can measure the battery temperature; not just the charger’s temperature. 🤒
Obviously most shop chargers don’t have this capability but some do have an AGM setting that is voltage controlled. Depending on the application, most vehicular or renewable energy charge controllers will have it as well.
The problem with charging AGM batteries without temperature compensation is that when charging cold batteries, the charge voltage tends to be very high. If a 12 volt AGM battery is charged above 15 volts (2.50 volts per cell) it starts to lose hydrogen that cannot be recombined as oxygen can. This results in water loss and dry out and shortens life since most AGM batteries do not allow for water replacement.
You are correct about lithium batteries. The lithium battery BMS will not only prevent charging at low temperatures but most will also limit discharging at low temperatures. If you have additional questions, please contact me.
Back to me…
Here’s an AGM-only charger from BatteryMINDer that can accept an optional remote temperature probe. You can find it on Amazon HERE.
Some of the products above have affiliate links. This means that, at zero cost to you, I will earn a commission if you click through the link and finalize a purchase.
According to Battleborn Battery CEO Denis Phares, Battleborn Lithium Batteries can be charged at a slower rate than 1c at temperatures down to 24 degrees F. Their charging profile says to not use temperature compensation.
Some NOCO smart chargers include temperature compensation…but the temperature sensors are embedded in the charger, not a separate temperature probe.
Also, though I do not have AGM coach batteries, the Renogy solar charge controller has an added temperature sensor probe placed with the batteries, as well as the Victron smart shunt.
Note also that some (if not many) modern vehicle chassis electrical systems include temperature sensors in determining and setting the chassis alternator output voltage. As an aside, some chassis manufacturers also recommend and have procedures to adjust software controlling the chassis charging system for AGM batteries.