Li-Poly Cells

Constructed of laminated sheet electrodes and separator. External pressure from a rigid housing is not required allowing a light weight foil packaging and construction to a shape to suit the application.

The technology apparently evolved from lithium-ion batteries. The flammable lithium electrolyte is held in a polymer composite. Advantages include lower cost and more robust.

Cells must not be charged above 4.235 volts or discharged below 3 volts. Overcharging results in swelling and a risk of rupture and fire. Discharging below 3 volts can cause permanently reduced capacity and increaded voltage reduction under load.

Problems within packs include differences in state-of-charge and differences in capacity between cells. Balance charging of cells within packs ensures maximum capacity and life expectancy.

The charge process involves applying a constant current of not more than 1C until the cell voltage reaches 4.2 volts at which point the cell is about 70% charged. The current is then reduced maintaining the voltage until the applied current is 0.1c or less; 100% charge. Balance charging controls the charge applied to each cell.

Some cells claim charge rates exceeding 1C. What this does for capacity and cycle life, I don’t know, and is probably unnecessary most of the time.

Some manufacturers recommend storage beyond a few months at 40% charge and refrigerated.


IMO with common sense and a bit of understanding Li-Po batteries are not  a significant hazard.

The majority of problems result from incorrect charging or physical damage.

You’ll be reasonably safe if you don’t damage or break the cell open and do not over-charge by applied voltage or charge at greater than 1C rate. I recommend charging at 0.5C although this takes too long for most people.

The people who tell me that Li-Po batteries are unsafe because they burst into flames when shot with a 22 or hit it with an hammer are morons. They probably check if the lawn mower is running by feeling for the spinning blade.


Lithium based batteries are supposedly environmentally friendly and once fully discharged (to 0 volts) can be thrown away.  Any more than a few cells should probably be handed over to a recycler to deal with.

Some info I have read suggests that when Li-Po cells are completely discharged, the metal lithium is converted/consumed and the cell is no longer a hazard.

Another suggestion that I haven’t confirmed recently is that if a cell is fully discharged and then broken open in salt water it is rendered safe. Without confirmation I wouldn’t recommend this.

I  have fully discharged reasonable sized cells and then chopped them in half using garden tools…. Nothing happened…. Just make sure they are dead-flat first.