My AGM start battery failed me yesterday, and when I put it on the charger overnight it was stuck at a 65% reading. AGMs should charge much quicker than that.

To the internet....and found a great trick and solution.

The problem, according to the article, was that when the current reads lower than 10.5V (read 10.2), there may not be enough current flowing back to the charger for a good reading and to continue the flow charge. Apparently this is very common in AGM batteries and many, as did I initially, write off the battery as dead as it won't take a charge.

The solution was to parallel the AGM with a good battery, throw on the charger to the AGM, and let it run for an hour. Then, the AGM will have enough charge to accept the charger current. I used my deep cycle and it worked like a charm. Pulled the deep cycle connection after an hour, and within 10 minutes the AGM read 100% and the motor turned over easily.

The last step is to test the load, and that I have not done but did order a load tester. There's a good chance we boat people all have batteries lying around that we think are shot and may not be, and some of the batteries that have a good charge reading may not hold up long under a load. $28 Amazon.