I just experimented with a 12V, 140mA (1.7 watt) PC fan. Although it's not 30C here, I believe that if it were placed to blow over the bed it would be more than enough. I tried it on 5V, and that was also encouraging (less air, very quiet). It would be enough for one bed - need another fan for a second bed.
If you're only consuming 1.7W, then for overnight you need only 1 or 2 AH. I would recharge it with an ordinary wall transformer, about 150 mA, 13-14V.
If you're only consuming 1.7W, then for overnight you need only 1 or 2 AH. I would recharge it with an ordinary wall transformer, about 150 mA, 13-14V.