My motorcycle starter battery (flooded lead-acid YTX 12BS) 12V-12Ah developed this odd behavior of voltage increasing when resistive load connected.
Wanted to do a load test by connecting directly to battery terminals a resistance (toaster like) to discharge it at 0.1C (1.2A) and count the hours elapsed when fully discharged (to estimate the remaining capacity). Voltage on open circuit before connecting it was 12.75V. In just few minutes under the resistive load it was increasing above 13V, (seen a max of 14.2V after ~one hour).
Can someone please explain why this happens? Is the battery nearly dead or deflective somehow? When trying to use it to start the motorcycle, sometime voltage drops below 9V while cranking (most of the times stays at 10-11V though).