I'm using a Turnigy 4x6S 400W Lithium Polymer Battery Charger. I know is expensive but use it to charge in the 'field' as it is 12v input, so if you want to use on mains power you would also require a 12v power supply. I always prefer to charge individual batteries with separate outputs just in case of one battery/charger developing a fault as explained above. When away in caravan with no mains hook up, I just connect to the two 115 A/h batteries which are topped up with a couple of 80w solar panels. I bought 4 of the internal dji phantom 2 power plugs, soldered new leads on the ends to fit the charger, 4mm and the monitor plug. Set the charger to 'lead acid' 6 cell type of battery at a charge of 4 amps, as the battery is smart and does all the 'lithium' work and regulates the current etc. It is nice to be able to monitor the batterys from the charger display, this charger also saves you buying a dji 12v car charger which costs £79 in the uk, again saving money. You do not have go for the turnigy charger I went for this model as it is 100w per output, you only need 50w for charging the phantom. The charger is a bit noisy due to the small fans installed but I mostly charge outside, on work bench or the boot of the car and caravan awning.
I have also offset the cost of the charger as I also use it to charge makita 18v 1830 batteries that will not charge in the original charger, these batteries cost £80 in the uk. Have had to take the batteries to bits and byepass the on board protective circuit and have fitted a 7 pin balance plug to the side of the battery case which directly plugs into the charger. Have also had to swap/solder dead cells but have managed to make 4 working batteries out of 5 up to now. My friends who have had dead batteries have just started to pass their dead batteries over to me now. Yes it takes a lot longer to charge the makita batteries but they are not getting as hammered as in the original makita 1/2 hr charger. The above is easy to do if you are ok with a soldering iron a bit of sence and more info can be found on youtube/internet on lots of different power tool battery replacements, please be careful
Regards Rich