The 11V batteries will likely rcover with just recharging but go gentle in the beginning. the 7V batteries are a different matter. I have only had 50% success rate when they go that low
My storage shed is also unheated and we get -35F sometimes for a week on end.
I have sucessfully recovered batteries of all kinds by first using the desulfators. Thaw out the battery then treat with desulfator for at least 24 hours then leave the desulfator in place begin charging.
My own preference is for the Pulsetech brand because I have not had any problems with any systems I installed them on over the past nine years. However now that the original patent has expired a number of clone products are out there. I am hearing good reports from people using these clones as well as Pulsetech users.
I have 6 8D 250 amp hr batteries at my off grid home that I dont live in yet. It is unheated. I snowshoed to the house last week and measured the Battery voltage of the batteries. The Voltage ranged from 7 to 11 volts. My question is should I be able to just recharge them after the spring thaw or are they toast? I have a generator and a large charger to charge them back up.