charging parallel batteries

[jltcym]

In an effort to increase the capacity of the battery I have supplying power to my electronics have put two batteries in parallel. When trying to recharge after use I don't seem to be able to get a fully-charged indication on my battery charger. I have tried 2 different chargers and neither seems to fully charge the batteries. The current charger I am trying is an automatic 10 amp. It started charging at 10 amps then after about 24 hours got down to 8 amps but now seems to not go any lower on it's charging rate. It's been 2 days.They are both new deep cycle batteries. When recharging I'm leaving the batteries connected in parallel with the electronics still wired in but turned off. Is it OK to charge like this? Also if it's OK to charge like this how should I connect the leads from the charger to the batteries? Thanks for any help that you provide.....Jim

 

[JB]

Re: charging parallel batteries

Hi, Jim.<br /><br />Automatic chargers decide when they have a full charge by reading the internal impedance of the battery.<br /><br />Two fully charged batteries in parallel look to the charger like one battery not fully charged.<br /><br />Your batteries are probably getting a full charge, but the automatic feature of your charger will not work.<br /><br />Good luck.

 

[Solittle]

Re: charging parallel batteries

Try charging them one at a time. Test with a volt meter before you put the charger on and again a day later. Works for me.

 

[jltcym]

Re: charging parallel batteries

Thanks for the quick reply. This was quicker than the Internet......Jim

 

[Jimwelder]

Re: charging parallel batteries

Your charge rate would be equal to no more then 5 amp per hour for two batterys connected as you have indicated from the 10 amp charger. Monitor the charging voltage also, it needs to stay 14-15v to overcome higher resistance caused by two Batt. in that circuit and base line voltage. To much voltage will cook them fast. Checking electrolyte level(s) and specific gavity prior to charging and afterwards along with battery voltage (12.5.5 to 12.65v) gives you best indicator of full charge(1.265+ sp.gr.). Battery tempertures factor into the specific gav. testing. Not known if yours are "sealed type, maintenance free" batterys. No matter the cost of most batterys, expect 3-4 years on avg for best reliance. Most auto parts stores could give those basic checks plus load testing for free. At 4 amps per hour charge rate, it could take 20+ hours on fully discharged battery. Jimwelder

 

[Arnold96]

Re: charging parallel batteries

You did not indicate that you have a battery switch installed. If not I would strongly suggest adding one. They are less than $20 and are well worth it. Ditto's on the other posts.

 

[Boatist]

Re: charging parallel batteries

Jim<br />Two batteries in parallel does not work very well. You would be better off to get one very big battery. The problem with two batteries in parallel is if a cell should die in either battery it will discharge both batteries. Having said that I also have two batteries. One runs everything the boat need to go, Starter, Trim and Tilt motors, Lights, Bilge blower, Bilge pump, Horn, Windsheild wiper, Trim Tabs. The other Runs all the electronics, Radio, Gps, Radar, Loran C, Fish finders.<br />Bateries charge in Parallel but thru a Battery Isolater. If one battery goes bad will not affect the other. Also have a battery switch to allow starter and boat to use second battery should first run down. Battery isolator does drop about .7 volts to both batteries but I have had no trouble with batteries. Mine have lasted about 6 years on average, much better than my cars and I do not know why.<br />I also use a 10 amp automatic charger to charge batteries and it works fine. The one I use just has a meter. You can set it to convential or maintenace free, and I always use the maintenance free setting setting for the boat. I ran two 10 guage wires to a plug on the front of the boat. Black wire goes to engine block, red wire goes to input terminal on battery isolator same as alternator wire. Reason I ran the plug up front was for two reasons. 1: I got tired of climing in under the cover and under engine cover or battery covers to hook up charger. 2: I have a 12 volt line that comes from the tow vechical and a plug that I can plug it to charge batteries while on the road. When I get home I always hook up battery charger and charge batteries while we unload the boat and clean the fish. I think this helps the batteries, as always use power after shut the engine off. Raising the motors, if at night leave the lights on until get everything put away and some times forget to turn off the electronic until in the tie down area. Takes about 15 to 30 minutes for charger to drop to zero. I also use charger about once a month in winter to charge batteries even if we have not used the boat. I have several battery charger but have not used the one that has the charge complete light. One I use has a meter and it will start at about 5 amps and drop to just off zero, less than 1/2 amp in 15 to 30 minutes after a day or night of boating. My boat is a I/O with a 40 amp alternator.