I'm not sure about batteries hooked up in series as I've never had a 24 volt system. As far as running two batteries hooked up in parallel, yes you can charge both batteries with one charger. You would want to hook the positive lead from the charger to one battery, and the negative lead to the second battery.

 

Yes.

Is this a 12v or 24v system? 12v you don't have to connect 1 lead to each battery but you can.

 

I have charged my batteries together by just hooking the charger to one battery. I have a battery switch in my boat that lets me choose 1 battery or #2 battery or both batteries. when I'm running I switch to both batteries so the boat alternator charges both batteries.
sherman

 

My boat has three batteries, two battery switches, and a two bank charger. The charger is hooked up to the hot lead on each switch and grounded thru the bonding / motors. So with the switches I can control which batteries get charged. Came this way from the factory.

My buddy has a similar setup but with two batteries, one switch, and a single bank charger. Again, his came that way from the factory...

 

I have charged my batteries together by just hooking the charger to one battery. I have a battery switch in my boat that lets me choose 1 battery or #2 battery or both batteries. when I'm running I switch to both batteries so the boat alternator charges both batteries.
sherman

This is the same set up I have. I also run with the switch on both. I'm looking to add a battery maintainer (1.5 v trickle). If I hook it up to # 1 batt. and have the switch on off will it charge both batts. Or do I need to leave it on both batt to charge both?
So in other words, when you have charged your batteries together by just hooking the charger up to one battery, what is your switch on?

 

with the switch in the off position the batteries are isolated from each other. to charge both batteries at the same time you need the switch in the both setting.
sherman

 

Sorry for the tardy response. I did not know the answer to the question and the boat iis stored off site. Got over there this morning to look at the battery. It is a Deka dc24 which ironically appears to be a 12v

https://batterywarehouseva.com/shop/deka-dc24-group-24-marine-deep-cycle-500cca-625mca/

 

A post in the following thread suggests two 12v won't double the operating time. Am I correct in my understanding that the switch kits I see online, where the user turns off one battery in lieu of the other, will rectify this?

http://www.ohiogamefishing.com/threads/battery-life.297858/#post-2173892

 

Here's some diagrams that may help explain (don't mind the green check mark and big red X)

Note the two 12v, 100AH batteries in the left diagram are wired PARALLEL. Positive to positive. Negative to negative. This leaves the batteries output at 12v but doubles the AH(running time) to 200AH instead of 100AH.

The two 12v, 100AH batteries on the right are wired in SERIES. This doubles the voltage output to 24v instead of 12v but the AH(running time) does not double. It stays at 100AH.


Here's a diagram of batteries wired together in parallel through a switch.
If position '1 battery' is selected on switch the battery voltage output stays at 12v and the running time is whatever AH just one battery is rated for.
If position '2 battery' on switch is selected, the voltage output from the batteries remains 12v but the AH(running time) would double...or what the total of the AH's of each battery added together (don't mind the 'starting' and 'auxiliary' written on batteries)

 

You want 2 near identical 12 v batteries with the same age and charge.You'll need 2 heavy guage jumper wires. Run 1 jumper to neg of each battery post and other jumper from + of each battery post. I'm thinking about this for my 12v terrova.

 

Much more clear now. Thank you

 

Why not replace the group 24 battery with a group 31 battery. You will get about 1.5 times the run time over a group 24 and reduce the weight by 33% over two group 24. Now you have less maintenance in checking water and charging is much easier. If running two batteries in parallel, one bad or weak battery can destroy the other battery.