Originally Posted by Maj_Overdrive

Get a lawyer of your own. I'm not a lawyer but it sounds like this is going to come down to picking apart the lease agreement and possibly generally accepted as well as lipo manufacturer safety practices.

All rc battery manufacturers put "never charge a battery unattended" on the labels of all battery packs. I'm sure that'll be one of their arguments and could constitute negligence of some kind. Your lease may not specifically prohibit charging batteries, but it may state that doing any activity in an unsafe or negligent manner will put you on the hook for damages as opposed to a purely accidental incident like an equipment malfunction or accidentally knocking something over. This is where you need a lawyer to go over your lease agreement. The insurance companies will also be more likely to accept a settlement (which is likely what they're looking for, anyway they can minimize loss is good for them) after you've retained legal counsel.

Edit: Other arguments in their arsenal could include other "generally accepted safety practices" like the use of a lipo bag or other fire resistant container, the material of the surface you were charging on, etc. Anything you may have done wrong or that could've resulted in damage that is greater than if you followed generally accepted safety practices you could be held liable for due to negligence and/or incompetence.