It's been in the mid-low 20's here in North GA the past few mornings. Yesterday I tried to start our semi-retired '00 Mountaineer 5.0L (265,000 + miles and counting) and it's already weak battery had bitten the dust. I decided that putting an expensive battery in this old gal just didn't make sense. I checked AutoZone for a cheaper (but decent) battery and found they wanted $99 for their ValuCrap group 65 battery, which only came with a 12 mo warranty. I considered their "red-top" battery, which was $140 and now only comes with a 2-year replacement warranty. I checked TSC (too expensive). I checked Napa, $99 for their Legend battery that I think had a 2-year replacement/75 month prorate battery, but I've never got more than 4-5 years (at best) out of 3 previous Napa Legend batteries. I didn't even consider Walmart. Then I recalled that Home Depot sells auto batteries and I'd just gotten a "$5 off any purchase" coupon. Home Depot sells Excide batteries, which are a pretty good brand. They had 850 cold cranking amp, Group 65 batteries in stock for $99 with a 3-year replacement warranty (less the $5 coupon). There were also lots of excellent customer reviews. So this was a no-brain-er. I'd installed a Home Depot Excide brand battery in my hot-rodded 12V '54 F100 about 3-4 years ago. This truck is rarely driven (maybe 5-6 times a year) and that Excide battery has never even required charging after sitting for 6 months (the previous Durlast red-top batteries I'd had in it were noticeably weak after just a couple of months of inactivity).
So, if you need a good, inexpensive battery for your Explorer (and many other Fords), consider Home Depot Excide Group 65.