6. EXTERNAL MECHANICAL DAMAGE - it doesn’t matter if you have the highest quality cells in the whole world if you dent your pack. In order to understand how mechanical damage affects a lithium polymer battery – you need to understand how they are mechanically built. A lipo battery is made up of 20-30 layers of a very thin sheet copper anode, a thin plastic separator and a thin aluminum cathode. A dent will can create a microshort by making the stiff metal anode or cathode poke through the soft plastic separator. As I mentioned above – this microshort will create an area of localized heat. If you are lucky – the cell will puff up. If you are unlucky – you will have a fire hazard. Another repercussion of a dent is that some layers of the cell will become delaminated and thus inactive. This means that the working layers will need to work harder to provide current and thus generate more heat in a localized area. I’ve been a huge proponent of hard cases to protect the physical integrity of lipo cells. In my professional opinion, a hard case for RC cells should be mandatory. I cannot believe that there is at least one lipo battery distributor that is spreading propaganda that hard cases for lipos are not good. In my opinion, this is absolutely irresponsible. Toshiba had a recall on laptop batteries when they found out it would not withstand a drop test. The soft-shelled lipos don’t stand a chance in a drop test.

I’ve seen many postings on how XXX user has a soft shell pack that’s been ejected from the car and run over by another car and there was no fire and therefore hardshells are not required. Great – lucky you! Most of the time nothing will happen – but you don’t want to be around when that 1% of the time when something bad does happen. I’m surrounded by thousands of lipos everyday, but I wouldn’t pit next to a racer running a soft cased lipo.

What can you do? If you are a track owner/operator – insist on hard cased lipos.
As a governing body like ROAR – start specifying rules for the hard case. For example, the hard case needs to have a seam so that in case the cell expands, the case will pop open so that the cells do no build up any more pressure. In my opinion – Orion did a fabulous job designing the case (except that they flopped the + and – going from the 4800 to the 3200 battery) and I hope others copy it.