Re: Capacitors. If you're concerned about them failing you can 'reform' them. I would suggest the simplest way of doing that in your case is to switch the PC on for a few seconds - before it goes into it's boot routine, then switch off. Do this a few times over a couple of hours and it will help enormously.

Re: Batteries. It's most likely the batteries are 3v Lithium, probably CR2032 coin cell types. 2032 means 20mm dia x 3.2mm thick. Lithium cells have a very long shelf life of 10 years or even more. Cheapest place to pick them up is you local 'cheapo' supermarket or a market stall. I bought some recently for 35p each.

Soldered-in batteries tended to be rechargeable 3.6v (NiCd or NiMH).

John