Recently I bought a used Syma X5c with many spares/etc on eBay. I got it flying - briefly, anyway - and for the $15 I paid, I wasn't even expecting that much!

I've got about a dozen batteries and two of those little black USB-to-5x batt chargers. Half the batteries are puffy and I put them to one side for proper disposal right away. The rest - well I don't know if the chargers are even working, the lights are either all on or all off, or flickering, but bear no relation to how many batteries are plugged in.

The batts measure mostly in the upper-3v range, some change after being on the charger awhile and others don't, but even one I got over 4v won't start the drone (it's stuck in fast-blink mode). The one that did work, ran the drone for about 2 minutes. For all I know the whole thing could have been on the shelf for a year and it was the last battery that had held any charge, and the chargers aren't really working. Or, all the batteries could be used up - it's clearly seen a lot of hard use.

Is there a way to properly test these batteries? I can look up charging specs and charge them with my bench supply, then - put a resistor in circuit and watch the voltage drop, maybe? Is there a simpler way? I have a USB-to-battery charge cable for my Syma X26 but it won't fit the X5 battery plugs, so all I have for now is those little junky 5-battery chargers, which weigh nothing and seem flimsy anyway. Hard to tell if they're doing anything!