One battery sometimes sags way more than the other

[Mikhail K]

Hi all. My LV Centaurus DNA 250C mod regularly sags one battery significantly more than the other under load.

I.e. both batteries have an idle voltage of 4.2V, under load one drops to 3.94V, the other to 3.71V. Then, when the load is stopped, they return to the same voltage. Before the problem could be sometimes completely eliminated by swapping the batteries in the slots, or simply reinserting them, or pushing the mod from bottom to top so that its panels move (the mod has some play in the front panel and the battery cover when pressing with force, although all the screws are tightened). However now it seems it has no effect anymore. In fact, sometimes the same actions make the imbalance in sag worse.

No problems with the batteries themselves. Tested 5 “married” pairs, original P28A and P30Bs, the problems persists with brand new batteries, too. I wipe the battery contacts and all the contacts in the mod (including the balancer contacts) with alcohol - they are always clean.

Reddit suggested there may be a bad solder joint somewhere related to the batteries. Should I disassmble the mod and try to re-solder these connections?

[Wayneo]

Is it always the same cell # that sags more? Like, even if you swap the actual batteries, the sag does NOT move with the battery?

If those are a yes. I'd be looking at the JST connector or anything to do with that particular cell connection.

[Mikhail K]

3 hours ago, Wayneo said:

Is it always the same cell # that sags more? Like, even if you swap the actual batteries, the sag does NOT move with the battery?

If those are a yes. I'd be looking at the JST connector or anything to do with that particular cell connection.

Thank you, that's right, it's always cell 2 (the blue line) when this happens.