Charging 2 batteries at once?

[stuee]

Hi, i have a boat which ive installed 2 batteries, one for the motor and winch, the other for the electronics.
I get annoyed with having to remove things, lift the cushion and try to clip on the charger terminals then do the same for the other side.
am i able to hook the 2 batteries together and so when i charge 1 it charges them both, if so is there a way to stop the charge going from one to the other too.
I would like to put a solar panel on soon which ideally would keep power to both batteries and use an Anderson plug so i can plug in the battery charger when i get home.

any ideas. thanks

 

[Misterbenn]

Presuming they are both the same voltage?
Are they both referenced (connected) to the same ground, chassis for example?

 

[MikeMl]

I have two batteries that I charge on my boat at Lake Powell. One is a house battery, the other is a starting battery. There is also a starting battery on the beater truck I use to launch the boat. One 20W panel and one solar charge controller. I built a timer-sequencer to connect the charger to the three batteries on a one-hour-at-a-time basis.

 

[stuee]

Yes misterben 12v deepcycle and mikekl i have a 60w that i want to use as my starting and anchor winch battery takes a hammering.

 

[Misterbenn]

So you can get multiple battery solar charge controllers, which is an off the shelf option for you.

Or if you split the positive charging lead into two lines and put a low Vf diode (and about twice current rating of charger) in series with each line. Then the charger will charge the lowest voltage battery until they are balanced after which the charge current will be shared. This assume they both have the same ground point.

 

[MikeMl]

So you can get multiple battery solar charge controllers, which is an off the shelf option for you.

Or if you split the positive charging lead into two lines and put a low Vf diode (and about twice current rating of charger) in series with each line. Then the charger will charge the lowest voltage battery until they are balanced after which the charge current will be shared. This assume they both have the same ground point.

The problem with just using two diodes is if one of the batteries develops a shorted cell (I have had this happen), its voltage drops from its nominal 13.4V float voltage to about 11.4V. That prevents its neighbor battery from ever charging... That is why I switch the charger to one battery at a time...

 

[Misterbenn]

That's true, i hadn't considered that. Thanks

So it ideally needs something with integrated battery health monitoring. Or a simple if less optimal solution would be as suggested a timed sequence

 

[MikeMl]

That's true, i hadn't considered that. Thanks

So it ideally needs something with integrated battery health monitoring. Or a simple if less optimal solution would be as suggested a timed sequence

Since my boat sits unused for long periods of time, there is still plenty of time for all the batteries to come up to the correct float voltage.
I have thought about using a micro which switches batteries based on their respective voltages. It wouldn't dwell on a shorted cell battery, and it would switch to the next battery in sequence when the previous battery reaches the correct temperature-corrected float voltage. There would also be a upper limit on how long the charger would dwell on any battery before switching to the next one...