This happens a lot when an OP posts an electrical problem. A lot of good responses are given but most of the time in the wrong order. When troubleshooting (TS) any electrical problems you have to start with the basics and you should do it in a logical order. If you don't you will be chasing your tail.
You have two set of batteries (B+) your coaches cranking battery and the house B+'s. You first must check the voltage for each and all B+'s.
The cranking B+ should be 12.6 volts (V). If you don't have a digital volt Ohm meter (DVOM) you should get one. They are much easier to read in tenths of a volt. If any of the B+'s are not at 12.6 V then they must be charged. You said that you charged a B+ overnight. Do you know what the charging Voltage was??? If it was not about 13.6 volts then your charger is no good. You assumed because it was on the charger that it would charge but you don't know that unless you measure the voltage at the B+ while it is charging.
Even if the charging voltage is 13.6 V's the B+ may not be accepting a charge. Now why is it not accepting a charge?? You might have loose or dirty connections on either the positive or negative cables. Or the B+ just may be bad and not accepting a charge. The best way to determine that is to take it out and have it load tested at any parts store. They all can check B+'s because they want to sell you a new one. But before you take it in to be tested you have to check the water in the B+ and charge it for at least 24-hours with a known good charger. They test the B+ by applying a heavy amperage load 100+ amps for 15 seconds. If you charged the B+ for those 24 hours and it fails the test then you know ir really didn't charge. Load testing is the only way to determine if it can supply enough current to crank.
When checking cables you MUST check both ends of the cable and you must check both positive and negative cables. You should also check/clean/tighten all cables that lead to and from any solenoids in the circuit.
If you check these items out first you just might find your problem. Just because it started 5 times over the winter does not mean that there were not problems brewing. Maybe the charge finally reached a point where it just wouldn't crank the motor anymore.
Once you verify that all B+'s are accepting a charge and all are charged and that you've cleaned and tightened all the heavy battery cables and you still don't crank then you may have a solenoid that is internally corroded and will not allow enough current to pass through to crank the motor.
Sorry this took so long to explain but it just does. Remember don't skip steps and perform these in order unless you like chasing your tail.
TeJay
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