I recently had two of my best Lipo hard packs look to have expanded already. I have an Associated 5000/40C and a Orion 5000/45C hard packs, both are just 1 yr old. I do not abuse these packs, charge them as recommended and have Lipo protection ESC. I only use these packs for racing, 17.5 on-road. They have not been used more than 25 charges each.

Why would they look to have expanded already.

In contrast I have Orion 3200 ( purchased in 6/2006)' Orion 3400 and Orion 3800 ( purchased in 2008 and 2009) all hard packs and charged with over 100 charges each if not more and no problems.

Did the chemical makeup of the Lipo change and reduce the reliability with these higher rated packs or is there another problem?

How much charge did they have when you stored them?

Sometimes full, sometimes partial. I treated these batteries same as my others.

You were duped with lemons... Lipo would only behave like that if they have been over discharged.

There are a number of reasons a lipo cell puffs. The top 3 (in order perhaps) are

Over current discharge (with subsequent overheat)
Under voltage discharge (going way too low)
Spending a long time at or over full charge

The first two do not apply, the third does apply - I have stored these batteries with a full charge, but I have done the same with my other lipo batteries in the past and no puffy problems.

I did contact Associated yesterday and they said a small amount of puff in the pack was normal, as long as the case was not separating, which mine is not, it only seems a bit firm/expanded in the center of the case.

I tried to find a number to call for Orion, but they have no tech / customer service contact numbers on their website.

I am still looking to get a firm answer - are these higher capacity packs more sensitive then the older lower capacity packs?

I have heard Jim Drew state that the new 65 or 70C packs will puff within hrs if left fully charged. I imagine that perhaps newer packs may be more susceptable than older packs. I've left plenty of packs at full charge for much longer then recommended times and haven't noticed a thing different. I don't have any new 50 + C packs. My highest pack is an advetised 40C.