I just want to ask. I'm in the rent-a-van business, and I'm also the driver of a Toyota Hiace Grandia. I keep it running because of the hot climate, and I sleep here when I'm with a client. Sometimes I keep the engine running for two to three days, even when I'm not moving.
My question is, what can I possibly be doing wrong? What will break easily? I know I'm wasting diesel but I don't know about battery.
Having the engine maintain idle rpm for extended periods is generally frowned upon by many sectors of the automotive world. The primary reason for this is that it isn't the most efficient engine speed for most engines.
It also can be a cause for excess fuel left unburned at those engine speeds 'leaking' past the cylinders and contaminating your engine oil which may lead to unwanted wear. The additional wear on all associated moving parts means that you'll need to get them serviced or repaired that much sooner, negating any possible savings that you think you may be getting by choosing to sleep in your van. Granted the additional wear isn't something that happens overnight or immediately, but instead slowly happens over an extended period of time.
You are also introducing additional pollutants to your immediate area; pollutants which you yourself may be breathing in since you sleep inside your van. You are likely breathing in your van's exhaust gases without even realizing it. Beyond the cost of maintenance is the cost of your own health. Like aforementioned additional engine wear, the toll to your health isn't going to be immediately apparent. It will eventually manifest itself. No one should be in that position if it can be avoided.
Most batteries typically should last anywhere from 18 to 36 months with proper care. As long as you don't let the battery voltage drop below a certain point, there's not too much to worry about. I'd be more concerned with the myriad of bearings that keep parts rotating smoothly. Keep in mind that most bearings are in areas which leave much to be desired in terms of serviceability, and these could add to your potential problem.
Hope this answers your questions.
Thanks for writing in!