I'd recommend any "smart" charger to do the job. I have this charger but I got it on clearance from Tractor Supply as a store branded product for $40.
Supposedly the Schumacher chargers are good too. Basically the smart chargers usually have the following benefits; 1) They can tell you the SOC. 2) Have a "desulfate" function. If you're not familiar with lead acid batteries, "sulfating" is the formation of lead sulfate on the lead plates. Over time this forms normally in a battery but is accelerated during deep discharge states. It eventually coats the lead plates leading to the battery not working anymore. I think the "desulfate" function uses pulsed DC or AC to try and break up the sulfate. I don't know exactly how it works but it will only help extend the life of a battery some. It's not a magic cure all. This feature is usually automatic if the charger detects high internal resistance. 3) They ramp the charge current to optimize the life of the battery. 4) Most importantly a smart charger stops charging when the battery is full so you don't have to worry about overcharging it. Charging at high current is not good for a lead acid battery. For the best longevity you should charge at 2A. 10A if you can wait a little while but need to go soon. This likely won't harm the battery but isn't doing it any favors and 20A+ if you're stranded somewhere and need to leave ASAP. It won't kill the battery but does put some wear and tear on it. Another thing relevant to the FFE is that you probably want to unhook the positive battery terminal to charge the battery. The first time my FFE died I didn't unhook the battery and it fried my charger because the FFE was still trying to pull current for something. I suspect it was trying to run a coolant pump since when I unhooked the battery, bought a new charger, charged the battery and hooked the cable up it sparked pretty good and I heard a coolant pump run for a second or two. All you need to unhook the battery cable is a 10mm wrench or socket.
My FFE randomly died again this past weekend. Full charge Friday nite, two 4mi trips to and from lunch Saturday and parked, then Sunday nite it was dead, 6V dead. I tried a battery charger but the car was still pulling current and I didn't want to fry my charger again so I unhooked the battery cable and connected the charger to just the battery. After 8 hours the charger said battery was only 60% I gave it a 1/2 hour at 10A charge before I had to go to work, I forgot to check battery status as I had to go. I think it may be time for ford to replace this battery under warranty. I thought a previous firmware update fixed the battery issue. Apparently not.
I agree with EVA, you have to beware of the chineseium jump starters that may work once and only put out half or less than what they say they are rated for. There is a fellow on youtube AvE
who used to have a video up
where he tears down one of the "genius" jump starters and shows that it is total crap. I found another tear down of the same product but I won't put a link because I don't want to subject any of you to this guys annoying self righteous rants. Even with one of these crappy ones you'd probably be ok since all you need to do is power the computer and energize some contactors before the DC-DC converter takes over. I've had this Stanley lithium jump starter
for two years now. I've used it at least a handful of times to jump start ICE vehicles. Even multiple jumps between charges. Yes I can probably guarantee without looking that this Stanley unit is likely made in china too but at least it seems to stand up to some use and abuse. The unfortunate thing is that it doesn't fit in the glove box and since you cant open the hatch with a dead battery, I have to keep it on top so I can reach it by folding down the rear seats.