South TX, Free batteries, man you should be telling us how they run instead of asking. When I first bought my unit and my rechargeables were not delivered yet, I ran some basic alkalines in -5F. They didn't last the whole day in those temps, but I was happy with the performance when they were new.
Now, South TX probably doesn't have -5 F temps. I would grab 36 of those batteries and go have fun and see what you think. Three changes for the caller itself and two changes for the TX1000.
I did have some problems when I first bought my recharables on the first charge I put into them. MY fault in not understanding the particular Eneloop batteries that I bought and the new charger. Now the Eneloop XX batteries and the Maha 801 do a fantastic job in very cold temps. While I like my $175 investment in multiple rechargeables, FREE sounds awfully good to me. Free sounds like I would give it a try.