BTW "more convenient and cheaper" are strong arguments when you're in a competitive business. Lawn services are usually just a guy with a truck hustling for customers. The more lawns you can cut the more money you make. Anything that causes downtime such as running out of charged batteries is going to be a large negative.
I'd say your system is just undersized for your needs. Judging by having two batteries, it sounds like your system is one of those based around hand power tools batteries and then attempted to scale those up to lawn mowers. I've mostly heard bad things about this path. There's a lot of other experiences out there.
We started replacing them witg Milwaukee lawn tools. We frequently hit overheat cutoffs, but haven’t broken any yet. We do have a pile of dead small eGO and Milwaukee batteries though. These days, we only buy the biggest capacity we can. Those tend not to die as fast.
Electric is clearly the future for this stuff, despite our problems. The remaining gas powered stuff is all > 10HP.
We're talking a commercial mower though. I haven't seen prices yet, but I'd guess you're in the $15k range.
Robot lawn mowers are getting better, but I have yet to see one which can handle every situation that humans routinely handle.
