[ruslan]

Why not use a 5F/5V supercapacitor, DGH505Q5R5 or anything alike ? You may need to solder a 10R current reducing resistor in series.

[Denvercoder9]

Not OP, but with supercapacitors you're talking about a wildly different amount of energy. A 5F/5V cap stores about 62 J, while a 2500mAh 1.2V AA battery stores 10 kJ. With three of them you can store almost 500x as much energy.

[ruslan]

You don't need that much of energy to keep CMOS memory and RTC clock running. The battery will self-discharge way before it's exhausted by the load. IMHO.

[Kirby64]

Super capacitors have very high self discharge rates relative to a lithium battery. For something like an RTC which only uses a tiny amount of power, you’d quickly discharge the cap and have no way to charge it again.

[londons_explore]

What advantage does a supercap have over batteries?

[ruslan]

Supercaps don't not leak and do not require to be changed regularily. Yes, offline time on supercap would be small, a couple of months, but for a machine which is used often that is not a problem.