A battery can fail internally quite suddenly, producing full no-load voltage (DMM) but near-zero current when loaded. We've seen it multiple times.
Many years ago, early eighties ~ mid nineties (before the interwebs, AGM and LiIon batteries) an article appeared in Sportbike Magazine re: SBFS (Sudden Battery Failure Syndrome). We've looked for the article a few times since then since & haven't been able to find it. The article addressed the situation in which an apparently healthy wet cell battery will be fine one moment, then inoperative the next. We've seen it ourselves a few times, specifically with YB14LA-2 and YB14A-2 batteries (Z1's and '91 - '03 CB750 Nighthawk's respectively), always with batteries only 1 ~ 2 yrs. old.. Testing with a DMM will show battery voltage but, load testing reveals a battery that makes plenty of no-load voltage but cannot produce any significant amount of current under load. The problem identified in the magazine article was a buss connector between cells that would crack open. It was identified in the article as existing in U.S.-produced Yuasa batteries sold under a variety of brand names (Interstate, Diehard and others). Our experience was, battery would be fine, then turn on lights or attempt to crank, there'd be a 'SNAP' from under the seat, then dead bike. Full batt voltage on a DMM, no current / fractional voltage under load. Weird...
Since then, we've studiously avoided any bike battery made in the U.S. We've never had any problems with Japanese, Taiwanese or Vietmanese wet cell batteries, all of which die a predictable, gradual death at 4 ~5 yrs. of age.
What we think we've learned is, the only battery test one can count on is a load test.
Good Ridin'
slmjim & Z1BEBE
