I have 4 new GNB 650mah batteries for my Mobula 7 and the first couple of flights were really good, over 3 minutes. Long life and well controlled.  The last few I've seen massive battery sag and short flights, like around a minute.

Batteries were always placed on storage charge, used within a day of charging.  I was flying them down to 3.2V and as soon as I stopped flying they were bouncing back to 3.8-3.9V.

Today they were flashing low battery almost 20-30 seconds after take off, but then recovering to over 4V when landing.  I was pretty confused and didn't think I could have fried the batteries that quickly with the care I was taking.

On one flight I managed to disarm in the air and land on in my lap, which surprised me! I grabbed the quad and something on it was really hot.  I checked the motors and all felt cool.  I was checking it over and realised the jumper wire was warm.  I tweaked it and it broke off at the plug!

I gave it a try on 2s with the "spent" batteries, to remove the jumper from the equation and it flew like a champ for a couple of minutes more!

I depinned the jumper and spent a while trying to solder a wire into the tiny plug with no joy.  Then I realised I had clipped the tails off all my puffed 1s LiPos and the connector was the same, so I stripped a tail back, soldered it and heatshrunk over the soldering.

I popped in one of the batteries that was giving low voltage warning, but resting at 4V.  I managed to fly another 1m 10s before the low voltage warning appeared!  Result.  Will try some full packs tomorrow but looks like it was massive sag from the thin jumper wire with only one strand, rather than the LiPo's.

Orignal/broken jumper / 1s battery pigtail / soldered&heatshrunk version


Also note - the jumper wire is tiny compared to the battery tail, but in "1s" mode obviously all the current passes through the jumper, so perhaps this is even an upgrade.

I got into quads to build my electrical knowledge - something is sticking as I seem to be understanding, troubleshooting and fixing!  Happy days.

Another thing to be aware of is that the "pressed" (hollow) pins used in most JST connectors are known to be restrictive thus preventing decent current flow which causes premature voltage sag. If you want the maximum performance out of LiPos with JST connectors on it is worth replacing the connectors with ones that have solid pins. Have a read of the following post and the ones directly after it...

https://intofpv.com/t-eachine-trashcan-7...9#pid58769