Keeping the small 12v battery typical of hybrids charged has raised concerns if you only do short ,infrequent journeys .
But bear in mind that ALL recently made cars with petrol or diesel engines ,even those with large batteries to start large engines, are also at increased risk of a flat battery compared to a few years ago. They can go flat in a surprisingly short time if the battery isnt regularly topped up by being driven or trickle charged.
Its because cars now have an increasing number of computer systems, alarms, transmissions to keyless entry systems ,connectivity etc that are constantly active, 24/7, even when the car is locked and idle. The draw may be small but it adds up over time.
The good news is if the car has easy access to mains power, there are smart chargers that can be left connected to the car for long periods to keep it trickle charged. You probably wouldnt need to always have it connected, but its not a problem if you forget to disconnect it. Also you can prewire the battery so the charger can connect easily using a simple plug connector, perhaps somewhere inside the cabin. Saves the faff of opening the bonnet and attaching crocodile clips direct to the battery.
Without mains power there is plan B . With hybrids the small 12v battery doesnt have the heavily lifting of cranking and starting the engine. So if it does go flat you only need to boost it enough to power up the computer systems . I think this is only about 30 amps, as apposed to maybe 300 amps required to jump start an engine.
For about £30 you can buy small 'jump start' powerbank . They are small enough to carry in a pocket or handbag. In an emergency this should easily be able to 'jump start' a hybrid. (They claim to be able to start a 'conventional' car ). They can also be used to charge phones etc.
Plan C is a solar powered trickle charger, which is independent of mains electricity. It might help , and again it could be wired for easy connection/disconnection.
I have all 3
. Soon after I got my Mk4 I knew it would not be driven for about 2 months in January and February. (no one available to start it during that time) I attached a solar charger. The car started no problem on my return, but might have done so anyway.
I have a powerbank jump starter for emergencies. Not yet needed in over 3 years. Also a mains smart charger, not yet needed.