I need a really good battery for long term use in a device I'm making. The battery will need to supply 1.5mA, and 5V max. I require it to last more than 2 years, so that equates to 2628mA hours. Where do I find batteries like this?
I'd probably have to point you to Lithium batteries, specifically lithium-manganese dioxide (LiMnO2). They are primary (single-use) batteries, but have a very long shelf-life (low rate of self-discharge). You can typically find them in 3V cells, so that could give you 2 batteries in series for 6V. Use an LDO voltage regulator to hold the output at 5V (which will add additional current draw to run the LDO), or just design your circuit to handle a small range around 6V (up to 3.3V*2 = 6.6V).