When I first got into flying I was using a whoop style quad that flew on a 1S LiPo battery, which means a single celled lithium-ion polymer battery. The kit I bought came with a small USB charger that would handle up to four batteries and took quite a while to charge them completely.
I soon upgraded to a parallel board that would do six batteries and had a DC wall converter that would handle 3 amps, USB 2.0 caps out at 0.5 amps for comparison. It was much faster and better but it couldn’t do one important thing. After flying, I basically had to charge the batteries back to full, and Lipo batteries have a much better longevity if they’re left charged to what’s called storage voltage, basically about half way charged at 3.8 volts and about 30-50% capacity. Technically I could keep an eye on the charger while it was working and stop it once the batteries hit storage voltage, but sitting and watching batteries charge is not any more fun than watching paint dry.
Unfortunately there weren’t any chargers on the market at the time that would do storage charging for 1S batteries. I was looking at a charger geared for higher cell-count batteries anyway as I already knew I was going to be getting into bigger quads, and I happened across a forum page that talked about making an adapter cable to charge 1S batteries on multi-cell chargers. The adapter works by combining all of the 1S connectors in series to make the individual batteries look like cells in a single battery to the charger. It didn’t look too hard and would be a good way for me to practice soldering.
To make one I needed 1S female connectors, silicone wire, a balance lead, and an XT60 power connector. The number of 1S connectors depended on the size of the balance lead. I went for a 6S to be able to charge as many 1S batteries at a time as possible. This did mean that I couldn’t just charge one or two batteries on an adapter like this, I’d always have to do six at a time and all six needed to be the same capacity.
Soldering these up in series involved soldering the red wire on the yellow XT60 connector and the red wire on the balance lead to the red wire of the top-most 1S connector.
From there it was just a matter of connecting the next black wire on the balance lead to the black wire of the 1S connector along with the red wire of the neighboring adapter, and repeating across all 6 balance lead wires until getting the the last one where the black wire of the XT60 is included in the solder joint as well. It was an ideal project for someone getting into the hobby and needing practice soldering. Especially when I forgot to slid the heat shrink over some wires before soldering them, so I’d have to desolder the joint and redo it with the heat shrink in place.
The last stage was to add some heat shrink over the whole adapter. This last bit isn’t to electrically isolate any solder joints, but just to bind all of the wires together and make the adapter easier to use.
Balance chargers like my HOTA D6 Pro Dual use the combination of the power and balance leads to make sure that all of the individual cells in a battery are charging evenly. This let me treat six 1S 300mAh capacity batteries as a single 6S 300mAh capacity battery and more easily charge, storage charge, or even discharge batteries than any of the options I had at the time.
Just recently there’ve been parallel charging boards that have come out that will do 1S batteries by adding a jumper from a balance port to a power port. This loses one spot on the parallel board but it means that the charger treats the batteries as a single 1S battery with five times the capacity, so the charger can push more amps and charge the batteries faster. It also isn’t limited by needing exactly six batteries like my original cable so I can charge anywhere between one and five batteries, since the sixth slot is take up by the jumper.