Well basicly the battery holder's come wired like this.
I add a large female tamiya connector to the battery holder leads and i bit of 3mm heat shrink to neaten things up a bit.
To be technically correct the positive wire goes on the left when the large single tab of the female connect is facing down and the two small separate tab's are facing up and the connector is facing away from you so the side the terminals slide into is facing you.
You will understand what i mean if you had a female tamiya connector in front of you, but as long as the positive and negitive wire match from the battery holder to the main charge cable it is all good.
Then i use 4 mm male banana plugs as this will fit all hobby chargers and 4 mm (16 awg) black and red silicone wire and 5 mm heat shrink and make a main charge lead like the one in the bottom of this picture below.
You don't have to use tamiya connectors you can use any plug of your choice or plug it directly into the charger, I do it this way cause i have many things that plug into that tamiya main charge lead so i can swap back and forward and i pick large tamiya connectors cause they are cheap, very common and Ive been using them since the 1990's, now they need a special crimping tool, Ive never brought one, i just fold and squish the pin,s over the wire with long nose pliers and then solder them its much stronger then crimping alone IMO.
Or you can buy a premade tamiya main charge lead but you will still have to add female tamiya connectors to the battery holders.
Female tamiya connector
Male tamiya connector
4mm banana connectors these are actualy bullet connectors but i like them better over the banana connectors as the wire is held in with solder so a screw thats easly strips but heat shrink is needed.
5mm black heat shrink
5mm red heat shrink
All items can be found on hobby king (apart from the battery holders) or ebay for dirt cheap you can make a few battery holders for less then a few bucks each and have parts left over to make up more charging leads for your hobby charger.
Ive posted all thats needed, the battery holders are only cheap and the wire they come with is only good for 4 amps maybe 5 amps top,s, Ive noticed no excess heat with 4 amp charges on my icharger, this should be fine and since they are in series the charge rate is the same as if you are doing a single battery its just the voltage increases automicly with the charger and the time of the charge is shorter.
I perfer to slow charge as many batteries as i can in a group, then fast charge them one at a time, slow charging in a group oftern works out faster then fast charging one by one and the batteries will last longer, take more mAh and the internal resistance will stay lower for longer.
Now for people using 10 000 mAh D cells 4 to 5 amp max might not be good enough, my D cells are only 5000 mAh and i only charge them at 0.125 c to 0.5 c but for AA, AAA and C cell,s it should be more then enough i hope this helps.