[EMS Discuss] LiPo battery recovery

Sat Jan 4 17:14:27 PST 2014

Just wanted to share a little thing I did that might help out.  One of my
sons flies R/C and an unfortunate intersection of hubris and forestry left
one of his planes stuck in a tree for a couple days.  The big-bad part of
this wasn't the heroic steps it took to finally settle on a PVC
arm-longerer to get it out, it was that the Lithium Polymer battery was
deep-discharged enough that the charger wouldn't recognize it and try to
charge it.

Deep-discharge is a killer of these batteries because the chargers are too
danged smart to try and do anything with them if one of the cells is below
a certain voltage.  This is part of safety circuitry that's part of the R/C
industry's aggressive 'don't burn down houses' strategy but can leave you
without when you need to fly.  It's happened to us before (a plane was left
'on' long enough to damage a battery, and these packs are kinda expensive)
so I wasn't looking forward to this.

I did some reading on the subject and learned about why the charger was
rejecting the battery.  I thought about it and speculated that perhaps if I
forced a little power in, it might get that rogue cell (or two) above the
critical threshold the charger is looking for.  I learned further that this
is risky so I did this with something between the battery and my
body/hands/face.  CAUTION: Be very careful when trying anything like this,
LiPo batteries are basically little bombs if mistreated badly enough.

The battery is a 1300mah 2S 7.4v 20C LiPo, for reference.
took a pair of mid-gauge power wires and ran them into the charge plug for
the battery.  Placing the battery in my ad-hoc blast box, I too the other
ends and touched them to a 9V battery (positive to positive, negative to
negative of course).  I held them in-circuit for maybe 4-5 seconds then
disconnected the mess and took the LiPo to the charger.  Plugged it in
and...  success!  It began charging.

Once fully charged, we did some tests on it then took it flying.  It
performed well, no measurable degradation in power.

So if you kill a LiPo with deep discharge, it may be possible to bring it
back to life but be careful.

- Ben
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