Battery Charging

[Dino]

Hi,
I bought a boat earlier this year and I have been relying on running the engine to top up the batteries. It has a standard lead acid 110ah cranking battery and an Elecsol Deep Cycle 115ah Carbon Fibre Domestic battery. At the moment I just have a basic 8A manual battery charger. I have brought the batteries home to give them a good charge. Is this charger sufficient to charge these batteries fully.
Both batteries were below 12V when I put the multimeter across them. I charged the Elecsol for approx 16 hours but the charge only came up to 13V. I read that these batteries should come up to 14.4V and a standard lead acid to 14.8V. Is that correct?

What is the best way to charge them and what charging voltage should be used? Should I use the high or low setting on my charger?

Thanks

 

[rafiki_]

When on charge, the battery voltage will show 14+volts. When you remove the charger, you should see about 12.7v, which will then decay over time. You really don't want the voltage to drop below 11.5v before you recharge. Your charger sounds ok, and a higher output will charge the batteries faster. You can get a battery condition metre from someone like ASAP for less than £30, which you can connect across the + and - posts. It is a glorified voltmeter, and is a useful device.

 

[VicS]

Charge them some more on the high setting.

An 8 amp charger is a little small for batteries that size. It'll charge them but may take a bit longer from a low state of charge than one with a higher output.

Aim to charge them until you can get a reading of around 12.6 to 12.7 volts after they have stood with no charge or discharge for 12 hours or so.

For best results invest in an automatic charger with a maximum output of say 12 amps. That will charge them more quickly and you will be able to get them more fully charged without over cooking them. Also because it will drop to a float or maintenance charge regime once they are fully charged you dont have to worry if you forget about them and leave it on for longer than necessary or intended.

Don't leave a discharged or even partly discharged battery longer than necessary before recharging.

 

[superheat6k]

A rule if thumb for the charge rate is 10% of the AH capacity, but optimum rates vary with the battery construction and the cycle type. A simple 8 amp car battery charger won't be able to vary the charge voltage to optimise, and its charge rate will tail off as the charge exceeds say 80-90% of capacity, but a long slow charge will more thoroughly charge the batteries than a quicker higher current charge. I would leave the 8 amp floating on the battery on high for a day or so, possibly longer, then as suggested leave to settle, then look for a voltage somewhere above 12.7 v