Best way to keep gas from getting stale when ICE is rarely used?

I have used sta-bile for lawn mowers but I’m not so sure about a Prius. Owner’s manual clearly states to use at least ½ the tank every 6 months (refuel at total of at least 5.3 gal. (20L) of fuel every 6 months). GM recommends premium fuel for Volt since they anticipated low gas use with Volt’s range and felt premium fuel would stay stable longer. I’m currently averaging a gallon per month and I’ll go well above that, especially in summer, but I'm wondering how Toyota decided that a gallon per month of gas use was adequate? They are effectively saying that gas can be left in the tank for a full year (admittedly mixed with newer fuel) and be OK. Anyone else think that’s questionable? Owner’s manual indicates it doesn’t matter if I add a gallon a month or wait and add 6 gallons after 6 months as long as I don’t wait longer than that. Is one approach better than other? I will take at least one very long trip each year and fully refuel tank and probably trips well out of EV range every 3 months or so. So, I’ll easily meet owner manual requirements. Still, I wonder what long term impact on ICE is if I routinely barely beat the requirement over long stretches year after year? Will I have a like new engine with only several thousand actual miles after 5 years or one prone to problems from infrequent use and running on years of stale gas?

To demonstrate this being a real concern, here are my results after my first 2 months of Prius use with 9 mile commute to work, max speed of 50 mph, ability to charge at work, and with kids now in college, and many activities and stores mostly in EV range. Yes, I know I just need to get out more but that’s more often in summer than winter.

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(I reset Trip A on last refueling but didn't reset EV ratio at same time). I bought PIP in Maryland during an east coast trip I was making anyway and drove it back home to Indiana. Above are my stats since then. My first 900 miles was mostly HV and at least got through much of engine break-in. It would seem to me breaking in the engine with only a warm-up cycle every 124 miles along with some occasional additional short use would be even worse. So far, it hasn’t gotten cold enough here to use ICE for my garage to garage commute, so I've only used ICE for longer weekend trips. I chose PIP over Leaf/Volt because it was lower cost, even after tax breaks, and met my range needs. I also better trusted Toyota reliability and preferred to eliminate any range anxiety concerns. Effectively, adding an ICE was lower cost than additional batteries in Leaf and I won’t be using either that often. I haven't posted my mileage stats yet as I'll have a few more months before I'll need to buy gas!

So, I think it’s a problem many are shooting for and will be a bigger concern with larger batteries in future. Any recommendations on best care for engine when normal gas usage is 1 gallon per month? Premium fuel? Sta-bile? Why does everyone tell me they wish they had my problems?

 

So, given how all over the map responses are, sounds like I should trust the owner's manual.

The key question remains how old can gas be in a PIP tank, before it becomes a concern and what is best way to care for car? If stale gas is just going to burn less efficiently, I don't care much. If it will be hard on the engine, hard to start, etc. then that's a bigger concern. If it's a non-issue, then I'm already following owner's manual recommendation by using a gallon a month. Every 6 months I should put at least 6 gallons in tank and not worry about it. If I haven't used 6 gallons then I should run in HV until I do. Why should I run on gas before that if it's not necessary, isn't that the point of a PIP? I'm just in obviously mostly uncharted territory and looking for helpful guidance on how conservative to be, but not getting much useful beyond shared concern from Priuskitty. What's the point in switching to HV mode after 4 months if gas will be fine for 4 years? The Volt automatically forces use of gas after one year, along with requiring premium fuel, so I don't believe it's entirely a non-issue. I assume PIP or Volt tank compare reasonably to a sealed metal jerry can, but I'm no expert there. The Toyota pressroom does say "A new low-pressure fuel-vapor containment tank system releases pressure in the tank for the engine to consume the generated vapor" so they apparently took some steps to help beyond a normal Prius. The Volt apparently has a pressurized tank and I don't know how designs compare.

Obviously, I can drive without charging and use up the gas. Seems like a real waste of expensive batteries that I'm carrying around unless gas is truly stale. The key question: Is there any evidence to suggest being more conservative than owner's manual requirement or is it wise to take any other steps?

Previously I would have considered premium fuel a waste of money. For 6 gallons every 6 months, that's only several dollars a year extra. I would readily do that if I knew it helped more than hurt.
Other more helpful advice might be to stop using the full battery range and switch to HV with 3 EV miles left so that at least I'm not discharging batteries as deeply and perhaps getting some benefit on battery life while also exercising ICE more. That's if I know I can't finish trip in EV mode as running ICE for only 2-3 miles is maximizing inefficiency. I recognize Prius doesn't use full range of batteries so exactly how much help it is to never go below 35% instead of normal 24-25%, I don't know.

I finally did find a year old gas stabilizer thread that raises concerns about using sta-bil and looks like the lack of knowledge on topic remains about the same. I already plan to take at least one 500-600 mile trip per year so I guess that's all I really need to do.