The NiCad batteries going dead is due to the nature of the charging system and the requirements of the NiCads. To get a long service life from NiCads they need to be completely discharged before being recharged. On the bike they are constantly being topped up without the discharge cycle. This causes the time to discharge to be less and less until they are worthless. I picked up a 1.2 Ah 12 volt lead acid battery that I'm going to stash under the seat. Lead acid batteries are quite tolerant of being topped off without being discharged. I'll let you guys know how it works out.
XR650R Plated Supermoto
XR628R Plated and highly modified
CR500R Still rips after all these beers
RZ350L Kenny Roberts Special
BMW R1200GS Adv Kind of a space ship