If your 4900mah pack really took back 4800mah, it is definitally damaged, it'll still work, but have much reduced capacity due to it holding voltage very poorly under load, it'll drop under 3.3v per cell before you get anywhere near expending 80% of capacity.
Hmmmm
I suspect your heli packs may have additional factors that killed them, such as excessive heat and current.
I's true that deep discharging is not "good" for the life of the pack. I think it's good advice to not run a pack "dead" (3v/cell) as a habit... but stick to the basic 80% rule of thumb.
But, you are a little carried away saying that a single full discharge "definitely" damaged the pack. That's kinda like saying he ran once with scissors, so he surely fell and stabbed himself.
well that sounded kinda funny to me anyway
If that was true then we would all have toasted packs... in fact almost every lipo sold in the rc market today would be ruined. Almost every ESC sold with lipo LVC would kill every pack, etc. Clearly it's not instant death to a lipo.
Consider: we have examples of packs that are just fine after even repeated "full dumps". For example, the SMC thread in the on road forum has results from a pack that has been cycled many times over several months of use. Each cycle is a full discharge to 3v per cell... essentially 100% capacity. Not only has this pack not died... but it's actually performing better now than when it was new. Runtime is down a little, but performance is actually better. Many of my packs have been dumped at least once without any apparent harm.
Also we have all the mfg data on cycle life of lipos at different depths of discharge, and they indicate reduced cycle life...not instant death. In fact I've seen info that shows almost the same total usable minutes during the life of the pack.
Ex: 80% discharge may show like a 20% reduction in cycles (500 @80% vs 400 @100%) but you also loose 20% of the runtime on every cycle. Total minutes of use is about the same. I don't have any real #'s but I've seen this basic concept in mfg data before on rcgroups.com
Occasional "100%" (3v/cell) cycles won't kill a pack.