Madasafish

Aircon seals dry out with lack of use..It is likely the entire system may have leaky joints..As Flash22 says, get it tested before spending anything.. It may be FUBAR in which case you are pouring money into a hole.. (and yes Kwikfit recharged yaris's system about 8 years ago and it is still working)...

Only if you are competent at DIY,,,

Thanks The comments on rust are spot on..

A decent battery charger will change charging current according to battery condition and can be safely left connected for weeks or months... Lead acid batteries sulphate the plates if left in a partially charged condition for a long time: capacity is then reduced.. Wife's Yaris is charged once a month in winter as short journeys and dark nights - lights, heater air con all one - can leave a battery in a partially discharegd state. I have a Halfords charger which self regualtes charge and works very well - idiot proof as if connected the wrong way it does not work and the warning lights on it go out..(just as well)

Too true. Rust in petrol filler pipe and rear sills meeting rear wheel arch are usual killers.

Yes

Chances are: the catalyst at the front of the exhaust has corroded and has holes in it.. Either the welded seams runing the length of it have split or the flanges mounting it to the exhaust pipe, (Son's one of similar age had that)

If the hybrid battery is fully discharged - which it will be - none of its compex electronics controlling how the battery is charged etc will work. You WILL need someone with the specific charger who knows what they are doing - and has done it before - to recharge it. If you get someone who does not know what they are doing - or who has not the correct equipment - there is a risk the battery or electronic will be damaged. £1000s repair bills.

Our 2003 Yaris D4D has its original exhaust. virtually rust free... It may outlive me .. Covid -19 permitting...

We are all getting old.. I use Petronas Syntium 7000 SAE 0W20 4 Ltr Fully Synthetic Engine Oil I always paid under £20 per 4 litres but the collapse if the sterling USD exchange rate will raise prices.. (2012Jazz)

Four quid a litre? Dirt cheap. See Castrol Edge prices and weep.

Sounds like dead fuel pump... you should get a warning code - low fuel pressure.

Did you check the battery earth cables at the body connections? It sounds like you have a faulty earth with resistance changing with current flow..

Check all the fuses. Check the battery voltage. Check all battery connections are properly tightened.

Blocked fuel filter Failing fuel pump (unlikely no warning codes) Blocked catalyst - do you do lots of short journeys..? Failing exhaust sensor (unlikely no warning codes) Is the battery original..? If so may be FUBAR.