Fellas,

How long should I be charging my trolling motor battery? It is a 12 volt system and my onboard charger is a 5 amp.  Also, I am fairly certain that my charger does not have any type of automatic shutoff when the battery is fully charged.  Is there a rule of thumb on how many hours I should charge the battery?  Also, can over-charging cause substantial damage to the battery?

Thanks in advance,

FD

How long a battery needs to be charged depends on how hard it was used.  It should always be charged within 24 hours after it has been used.  You probably should get a hydrometer from Wal-Mart or an auto parts store so you can check the specific gravity of each cell.  They should be around 12.5 v when fully charged.

Yes, you can over charge.

Voltage is not going to be a very good indication. While charging, the voltage is probably going to be over 14 volts. Depending on the battery, most good, fully charged deep cycle batteries will have approx 12.8 volts after sitting 24 hours after charging.

You will need either a hydrometer or a DC amp meter. Napa has a good hydrometer for approx $8 with the thermometer if it has removable caps. Specific gravity on a on most good deep cycle batteries is going to be 1.275 - 1.280

THe next option is a 5 - 10 amp meter (since your charger is only 5 amp) and connect it in series between the positive post and positive charger cable. When the meter drops to it's minimum current, charge for approx one more hour. To properly fully charge a battery, it should be overcharged approx 6 percent, that's why you continue to charge after the current drops to it's minimum rate. As a battery charges, the amount of current going into it drops, once it quits dropping it's charged, but as mentioned, it should be overcharged approx 6%, that's the reason for the extra hour.