I install them, but when folks move out I find that the smoke alarms are missing, batteries dead, etc. 

Most of them operate of a 9v battery and can hold a SD card.

There is really no limit to the possibilities of what you could get sued for.Most large liability claims are the result of a tenant repeatedly complaining about some danger;  lead paint in bad condition, no batteries in the smoke detector, not repairing a railing on a porch. 

Of course, check all smoke/CO detector batteries.  

The flip side to that is, even if you're working 80-100 hours a week, if you can see progress, things moving, getting closer to your goals, the anticipation & excitement of it can recharge your emotional battery like no vacation can. 

I carry a tool box and some ryobi battery powered tools with me, that's all I need.

In most cases it's the landlords, but there are items where the landlord and tenant may discuss and designate who wants to do it such as smoke alarm batteries, light bulbs, pest control, refrigerator water dispenser filters etc etc etc...Usually, if the landlord provided the appliance, the landlord is responsible for it's maintenance. 

One municipality requires both hard wired and battery operated CO and Smoke detectors in every dwelling be it SFH or Multi.This is why it is best to work with people that know the local markets.

That time spent left me no time to recharge my batteries, and more importantly spend time as the "visionary" to review and optimize my portfolio.

My channel manager has 2 AAA batteries.