from the guide, if you are interested. A cap will never leak (unless it's electrolytic and you install backwards. Boom!)
Memory Back-Up Capacitors.
If one insists on having a battery (can't live without those high scores!), I would recommend installing a memory back-up capacitor instead. These capacitors will charge when the game is on, and slowly discharge to keep the memory alive when the game is off. The advantage to these capacitors is they never wear out, and they won't leak corrosive materials. The best of all worlds in my opinion. Their down side is the game must be on for about one hour every month to maintain their charge (though I have heard them keeping a charge up to six months). Also, the game must be on for about several hours continuously to initially charge the capacitor. These capacitors are about the size of half a single AA battery. Jameco (800-831-4242) sells 1 Farad memory caps, part# 142957, $3.95 each, $3.49 for ten or more.
Installing the Memory Back-Up Capacitor.
After removing the battery and addressing any board corrosion, install the memory back-up capacitor. Drill a hole for the second lead of the back-up cap, just to the side of the negative battery lead (see picture above). Then mount the cap in the board, and bend the leads to hold it in place. Solder the cap in place. On the second lead which goes throught the hole drilled, solder a two inch wire. Extend the wire to the other battery terminial hole on the MPU board. Note the minus and positive leads were not labeled on the cap I installed. There was only a black line on the cap to designate the negative lead.