Charger
A web search for charger model YR-PF900CH05880130 produced no results. Similar chargers are about $100 on AliExpress.
The charger's DC-side connector is manufactured in China by WEiPU. It is their SP17 series which has an IP68 weatherproof rating (just short of the best IP69 rating).
Unfortunately, I am on my third attempt at buying the correct charging cable's plug/socket pair for experimentation. The first purchase was prior to having the bike in my possession. I bought a 2-pin connector because that's what the battery manufacturer pictured in their user manual.
Ah, it actually has 4 pins. But another failed attempt. My bad. I just bought the first thing I saw on eBay that had 4 pins. But that was the standard 1-mm pin diameter. The Dragonfly charger/battery actually uses larger 2mm (nominally) pins. This is designated by a B suffix in the part number.
It's interesting that 4 pins are used. There are only two wires inside the charger and the pins are not connected in parallel. I'm wondering if the other two pins provide communications with the BMS? It would be nice to be able to update the BMS firmware or get data out.
Left: standard WEiPU SP17. Right: Dragonfly WEiPU SP17
Charging cable (blue fittings) shown connected to battery
The charger circuitry is completely potted. I did notice a thermistor on the side opposite the cooling fan. I'm expecting the charger will shut itself off if it ever gets too hot.
End of charger removed to reveal 30A fuse (green)
Charger End-Cover Removed
This view shows several interesting things:
There are only two wires in the charging cable despite the connector having 4 pins.
There is a 30-amp automotive fuse (green) to protect again catastrophic failure. If your charger ever stops working it would be worthwhile to check this fuse.
The black cube is likely a relay to disconnect the charger completely from the battery.
Battery Charging Test
Prior to conducting this charging test, the 3.2 Dragonfly battery was discharged down to 42 volts (3.00 volts per cell). The battery then accepted 1652 Wh on the DC side. The power drawn from the AC line during charging was 1857 Wh. This indicates a charger efficiency of 89 percent.
Unfortunately, I did not have time to conduct an entire charging test but did not want to leave the battery in this low state of charge. Thus you will see a pause in charging after 35 minutes. I don't think this had much (if any) affect on the results and only mention it in the interests of full disclosure. Note that all the data in the following spreadsheet was taken manually.
The battery required 191 minutes to recharge. For comparison, my EM Race battery (having about the same watt-hour capacity) required 175 minutes. This seems reasonable since the Dragonfly's charger is rated at 12.5 A on the DC side whereas the EM's charger is rated 15 A.
Dragonfly Charge Test.ods