The battery in the C14 should be the AGM type (Absorbent Glass Mat). It is essentially a maintenance free battery in that once you fill it and give it the initial charge then seal it, you should never open it again. If you over charge it, you will damage it (short answer).
The battery charge voltage is higher (14.x Volts) while the charge cycle is active. Once the current to the battery drops below a minimum amount, the charger should shut off, and start monitoring the battery. Then if / when it drops below a 'maintenance level' (12.8V for AGM, typ.), start another recharge cycle.
Most of the "trickle chargers" out there will overcharge the battery if left on for too long (the ones that charge at 13.x Volts). They try to maintain a fixed voltage, which varies depending on the type of charger. The $5 (on sale) Harbor Freight trickle chargers try to maintain 12.65 to 12.75 Volts. They will actually bring down a AGM battery, since it wants to be at a higher resting voltage (12.8V), and the newest packaging on them states "Not for use with AGM batteries".
The Battery Tender Jr. uses the charge, monitor, recharge method. I have 2 of them in use, and would recommend them for your C14.