Battery storage and self-discharge

My lithium battery bank was removed from the boat in late October, 4 months ago. At that time, the batteries were charged to 100% and then disconnected and brought home. While they should be able to over-winter in the boat, I reasoned that 1) they were expensive to purchase and 2) they are rather light and relatively easy to carry. Spending the winter in a shipping crate in a basement, where the temperature swings are perhaps 5•C would certainly be better for them than in a fiberglass hull where they will be subject to wild swings in temperature, occasionally dipping into the colder side of -40•C. 

Anyway, the batteries were disconnected in to their 4-cell packs and brought home. They have seen no attention since. Last night, I decided to take a few voltage readings. I was pleasantly surprised to see that all 16 cells measured withing 0.001V of each other - 3.328V. Now I don't pretend that my cheap digital multimeter is capable of proving true readings down to mV precision, but since I was after relative voltage, the fact that it gave me the same reading for each cell gives me confidence in the data. They all settled on a reading of 3.328V. There were a couple of cells that hesitated between 3.327 and 3.328, but they did all ultimately settle on 3.328V. According to the storage discharge curve, that puts my cells around the 85% charge point. Right on track for 20% self-discharge over the 6 months of storage.