For a complete charge of a 12V LiFePO4 battery, a charger with a voltage ranging from 14V to 14.6V is necessary. If a charger with a lower voltage is used, it can still charge the battery, but it won't reach full 100% capacity.

Trickle charging is not acceptable for lithium batteries. Charging a LiFePO4 battery with a trickle charger not designed for this type of battery could lead to overcharging or damage due to the different charging requirements of lithium batteries compared to traditional lead-acid batteries.

Leaving a lithium-ion battery on the charger overnight should be safe if the charger is set with the correct voltage limit for the type of lithium-ion battery being used. For instance, with a LiFePO4 cell like the one used in LiTime Battery (with a nominal voltage of 12.8v and a fully charged voltage of 14.6v), using a charger with a 14.4-14.6v CC/CV output should work, provided it doesn't exceed roughly a 1C maximum current output. By following the CC/CV profile, ensuring the voltage is correct, and the current isn't excessive, you can safely achieve a full charge for your battery.

To determine your charging speed, take the amp hour rating of your battery and divide it by the output current of your charger. For example, a 100 amp hour battery (Ah) would charge in 100AH/10A=10 hours with a 14.6V 10A LiFePO4 lithium battery charger.

It depends on the voltages of your LiFePO4 lithium batteries. LiTime 14.6 volts charger is recommended for 12V LiFePO4 lithium batteries. And LiTime 29.2 volt charger is recommended for 24V LiFePO4 lithium batteries.