Here are some tips for using your AGM/SLA/gel battery in cold weather: Keep it above 32F (0C) as much as possible. Avoid charging when it’s below 32F (0C). Use a charger or charge controller designed for AGM/SLA/gel batteries. Many solar charge controllers have user-selectable settings for the various types of batteries. Lithium batteries.
Gel batteries are worthwhile since their performance is maintained throughout their lifespan. Its build custom, according to Battery University, produces a dome-shaped curve in its power output. There is no declining voltage, which is a common problem with other batteries.
Both AGM and Gel batteries (dry cell batteries) handle cold better then flooded batteries (wet cells) with respect to freezing, but as I said, a gel battery will pretty much stop working below freezing.
Gel batteries are a maintenance-free alternative to flooded cell deep cycle batteries. They contain a silica-based gel in which battery electrolytes are suspended, allowing electrons to flow freely between plates. The nice thing about spill-proof gel batteries is that they don’t leak even if the battery case is broken.
Gel batteries will not function correctly if their internal temp falls below 32 degrees F, so I suggest you purchase a trickle charger like a Battery Tender or keep the batteries in a heated building.
The freeze point of electrolyte varies according to the state of charge. Never allow flooded batteries to physically freeze. AGM/SLA/gel batteries have a similar cold temperature loss of capacity as flooded batteries. Freezing does not cause long term damage to AGM/SLA/gel batteries.