"Engine on, at 1500 rpms, battery reads 13.4; 30 seconds on the foot switch with no anchor load, 12.9." doesn't sound to bad. I would take the battery up to the windless and hook it directly to the motor. Eliminate the wire, switch and all the connections. It should spin the motor with the anchor for quite some time. You will find out if it's either a bad battery or bad motor. If, as you say, the battery is good you will find out if you have a high resistance in the circuit somewhere. As I said below, when you load a motor (as with putting an anchor load on it) the motor will pull more amps. Those extra amps will have to pass through various connections, contacts and lengths of wire. One of those connections, contacts or wires might not be able to carry the extra current without heating up. That will in turn cause even more heating until the circuit breaker trips. The breaker is most likely constructed with a by-metal strip. It consists of two metals laminated together. The two different materials heat up at a different temperature and the strip will flex and cause an over toggle condition that trips the breaker. This will happen when the extra current exceeds the rating of the breaker. The current in your case could be a bad motor or bad connections. If you don't have the tools and meters then putting the battery at the motor will go along way to help figure it out. It would be good if you could hook up a high capacity battery charger to the batter while it's on the bow working.