When batteries get old they can lose plate material, as when recharging the plate metal migration may not go back where it migrated from during discharge. This means you can lose plate area, which is where the big amps come from. It is also possible to lose 99% of the plate area in a single cell. There is enough plate to give a promising voltage. But, as soon as big amps are demanded, the voltage drops to near nil, only to spring back up when load is removed. Most battery supply sellers will offer to load test your battery to see what it’s condition is. They will charge it as recommended and then check voltage with rated load on the battery. If it passes that test, then I’ve seen similar maladies with poor connections, as in corroded, where the corrosion passes voltage until higher currents are demanded. That can appear to self heal too when load is removed. Make sure all your battery power cable connections are clean shiny and tight.
A friend had a CB400 that would randomly die. After some head scratching and exploration, I finally found the main power wire into the harness with a corroded crimp on a ring lug. Just bumping it would make the power go or come back…for a while. Sure enough, a confession that pot holes often killed the bike, but not after putting a new ring terminal on the solenoid where the main battery cable attached. The bike was then reliable again, and a smile appeared on my friend.
