Would a standard voltage regulator such as this on on Ebay Item no. 310281692683
Fitted in line with the positive lead from the engine, stabilise the voltage to more consistent 12 ish volts, or do I need something else.
Voltage in this range (16V) may be a little high and I would check this independently with a multi-meter as normal voltage is between 13.5 and 14.5/15V. If the voltage is too high it will eventually damage the Battery.
If you were only putting in 12 volts into your battery it would eventually become flat. Therefore the system has to generate more voltage than the battery's rated voltage to overcome the internal resistance of the battery and thus permit charging. The variance in the regulator is there to take account of the draw you are putting on the battery and the residual level of charge. In essence if you are drawing significant amps form electronics or draining the battery from constant short stop starts, this will result in a higher charge rate. It would also be useful to check the condition of the battery by using a high rate discharge or specific gravity test for each cell.
Ill hang up my cagoul now and all the best