I recently added an electronic optic to my AR (an EOTech) but I have dramatically curtailed my shooting due to finances. I've noticed with some of the tools and electronic equipment I own that use batteries that if left unused for a log duration (6+ months) the batteries will (sometimes) begin to leak and when I open the battery compartment I see the crusty battery acid/ooze. For tools/equipment I keep in my garage that use batteries I take out the batteries post use (mainly for things that are infrequently used). Normally I can just clean out the batter compartment, pop in new batteries, and the device will work fine. But this isn't a risk I am willing to take with my $300+ EOTech. I typically use Duracel batteries, and in my EOTech atm are Duracel Ultra (Lithium) 123 batteries.

Question #1 - What batteries do you use for your optics?
Question #2 - Good to remove them from infrequently used electronic devices?

Thanks!

1) For AA devices, I use Energizer Lithium batteries.  Everything else uses either CR123 lithium or whatever the Aimpoint ML2 uses (forget the size, but it is also lithium chemistry).
2) I don't think lithium batteries are as prone to leakage as alkalines, so for me, I don't.  I do remove alkalines.  I'll check my eotech in the safe tonight.  

Answer # 1: I use Duracell 1/3N on my Aimpoint and N type on my EOTech.

Answer # 2: Yes, it's a good idea to remove batteries from any devices when not in use for long periods of time.

I use my optics and lights all the time so they're always loaded with fresh batteries, also I always replace them before they're worn out, plus I always carry spares on my AR either in the battery compartment on my optic mount or my MIAD grip.

I'm a long time Aimpoint owner for 21 years and I never had a battery leak with my old Aimpoint 2000 which I use all the time, same with my current Aimpoint and EOTech, I would expect leaks to happen but it would be a rare possibility so I don't worry too much about it.

My Aimpoint CompM4 has a regular old Duracell in it. I leave it on. Since it's never not in use I just check it from time to time. 80,000 hr life on the battery supposedly. I figure I'll change it every couple of years.

One thing I can say is NEVER use Alkaline batteries in your Eotech.  The Lithium ones have been OK in mine for the past several years.