Hi Panther, Did you get the problem sorted out? It is definately the battery, no question. Voltage drop to 5 volts and clicking starter motor are classic indicators.

It should not drop below 10 or 11 volts when trying to start the motor. Testing the voltage while the engine is running will only tell you if the alternator is charging.

All reputable battery places or auto electricians will test your battery for free.

If you still need to buy a battery I have found Bursons to be the best for price on century batteries

Cheers Ric