Hi Scottie here
go to a hobbie shop
buy a RC car/truck battery cut it apart and make it to fit your case
the rc battery setup is wrong physically but you can rearrange them to fit in the cateye case .buy a 6 volt one,or 7.2 and use one less battery. should cost less than $20
each on is 1.2 volts 1.2 times 5 =6 volts
the pictures are of a laptop battery taken apart to make a 7.2 volt running battery for my puch maxi lighting and replaced dc horn ,and taillight(brakes)
Scottie Out :)