[everything.imp]

If GM is only going to lower the battery down to 30% charge why not just use a smaller battery. Which would cut back on cost and have it discharge down to say 10%?

I edited this to throw in the possible reasons I came up with. Maybe the most efficient way to prolong the life of lithium batteries is the method of charging they are using? IDK

 

[Altazi]

In general, the lifetime of a rechargeable battery is inversely proportional to its depth of discharge. A smaller battery with a lower DoD value would have be likely to have a shorter lifetime.

 

[JoeReal]

Deep Cycle batteries is what you'd call them. I used to have one for my electric trolling motor when fishing. Deep cycle batteries need to improve, then we don't have to carry a lot of dead weights around.