A stock KLR comes from the factory with a wet cell battery that requires regular maintenance. There's nothing wrong with this kind of battery, as it's inexpensive and fairly reliable as long as you regularly check and maintain the water levels in each of the cells. Unfortunately, the battery mounting position on a KLR only exposes one cell, so many owners never disconnect the battery, remove it from the cradle, and verify the water levels in the five other cells. This leads to batteries that are boiled dry, dying a quick death.
Aside from the maintenance issue, however, is the problem of leaking acid if the bike goes down on its side (or gets upside-down!). There's a clear drain tube from the battery to the underside of the swingarm that's supposed to route any acid or moisture that may leak out, but the reality is that if your bike is going to see some unusual attitudes, your battery is going to leak some acid and most of it won't make it into that tube. That acid spills all over the place and will make things ugly quickly, especially if its leaking onto you as you're trapped underneath your bike.
So, expecting to fall frequently while adventuring in the dirt, I replaced my stock battery with a sealed AGM (Absorbed Glass Mat) battery from Yuasa (model number YTX14AHL-BS). The local price was a little less than $70. Unfortunately, Yuasa has quite a few names for batteries that are of AGM design, but basically any battery of theirs that you don't have to add water to is an AGM design.
What's the advantage of AGM? AGM uses fiberglass mats between the lead plates in the battery to soak up the acid and prevent the plates from touching. Plates will touch and short if the battery is handled roughly (think lots of off-roading) unless a mat is in place. The mats also help stabilize the acid and make it less likely to leak out even if the battery is upside-down or on its side. Once you add the acid you permanently seal the battery and you never have to worry about water levels—or acid leaking out after a spill. Yea! One less maintenance item and a safer design to boot.