The point to Lithium is more than shelf-life - Alkeline cells perform poorly in cold temperatures. Lithium would be much preferred in very cold (well below freezing) weather.

I've never seen a datasheet on the Eneloop batteries and I don't know how they perform at low temperatures.

Some of Garmin's units use (internal) Lithium-ion batteries, and I assume many aspects of Garmin's products are shared (i.e., you do as much of the engineering as possible once to fit the entire product line and then customize for each individual product at the end - each product is not a clean-sheet effort). So parts of the design probably are intended to work with Lithium-ion, but not all, and it slipped through the cracks.

Garmin's reply on the Lithium issue sounds to me like a weasel-way of saying they screwed up. Someone forgot to actually *test* it before shipping.