Hi Mike,
The back-up capacitors used in this case, are of the Tantalum type. They are 1 Farad 5.6 Volt and are connected to the 3v3 DC supply line. I have never yet known a capacitor of this type to leak, since they use a solid dielectric. And of course, they are very low voltage types and not subject to the 'strains' imposed on the higher capacity electrolytic types, commonly used in power supplies.