Those are good conditions for running a hybrid and you would save fuel, but you would want to add a few longer journeys for keeping batteries charged up.

You don't need to do that at all. The battery on a self charge hybrid is small, deliberately so to charge and discharge quickly, so no need for longer runs.

Should have said battery, not batteries. The main hybrid battery will be OK. For Toyota Hybrids, there have been instances where the small 12v battery can run down if left too long or used on continual short journeys.

Got Mazda 5, 2013 has 52,000 miles. Nice car, runs well with sliding doors. Thought had it for 6 years. I’m spending quite a bit on petrol, thinking whether it’s time to change to a hybrid. Would it save petrol having a hybrid. I would probably look for a car, about two years old.

If you are not doing many miles, you can't be spending that much on fuel. It is also easy too forget that there is more to the running costs of a car than how much fuel you put in. Nothing likely to go wrong with a petrol engined Mazda, so hard to beat for overall running costs long term. Used car prices are of course crazy at the moment with no sign of imminent change, so the cost of changing to a hybrid (you haven't given a budget?) will be prohibitive and would undoubtably cover many, many years worth of petrol. So unless a problem with the Mazda, sensible thing to do would be to stick with it.

Those are good conditions for running a hybrid and you would save fuel, but you would want to add a few longer journeys for keeping batteries charged up.

You don't need to do that at all. The battery on a self charge hybrid is small, deliberately so to charge and discharge quickly, so no need for longer runs.

I'd very much echo those comments. It's likely the OP will get somewhere around the £5.5k - £7k 10yo Mazda (depends on condition and the engine) and whether they would sell privately or PX (looking on autotrader for equivalents for sale) but would likely have to spend well in excess of £20k for a 2 year old equivalent (mild hybrid car of the same size/type), never mind a 'proper' self-charging hybrid or even PHEV, which might take the cost to nearer £30k.

If their existing car suffers from no major problems and still drives well (as my older Mazda3 does), then spending a little occasionally on 'fettling' or wear and tear items and 20-30% more on fuel on a low base mileage is a price worth paying. They'll never make the price to change back (likely upwards of £13k) over the ownership period.

If and (hopefully) when prices of cars 'return to norms', then it might be worth a second look if the Mazda5 starts giving expensive trouble, but a well-kept example with the 1.8 or 2L petrol engine should be fine long term if you can keep rust at bay.

Finding a modern equivalent with handy sliding rear passenger doors isn't easy these days.