Batteries are relatively cheap. The meter will start giving errors when the batteries get low. I'm currently using Duracell, but may spend a few more dollars on the Eveready Lithium -- they should last longer -- especially when they don't get a lot of use. As far as leakage, I don't know.
I used to get 24 or 48 strips at a time - now I get six at a time and am grateful. If you live in a country that switches from Daylight Savings to 'standard' time, it may make sense to switch batteries whenever the time changes - or perhaps just remember to switch at around six month intervals (although batteries can probably go a year or more without leaking). For a few extra dollars a year, this may be a good way to reduce the risk of battery leakage in your meter.
I have some meters that I don't use often and DO remove the batteries, replacing them when I want to start using the meter - or using it to validate results from another meter - it just means setting up the time and date and data you want to see on screen. I'm going to start switching every six months so, out of an abundance of caution.