Dual battery solar panel controller advice wanted

Apr 26, 2017
I just fitted a dual battery solar panel controller (this one)

Should the voltage on batteries one and two not be the same when the solar panel is producing power?

I have my aux battery as the main priority (number 1) and it shows as fully charged so it should then charge the car battery.
My aux battery show as 13.4 volts but my car battery only shows 12.4.
Before this I had a single battery controller and it was normal for the volts to show 13 or 14 volts while the sun was out.
Apr 26, 2017
I have both of the the (-) battery connections on the controller joined together with a short wire then one of the (-) connections also has a long wire going to the (-) terminal on the aux battery which is joined to the (-) on the car battery.

Is that ok or do I need a wire from each (-) on the controller going directly to each battery (-)?

I've tried changing the car battery to be the main priority battery (number 1), but the car battery always shows as between 12.1 and 12.2 volts and the aux battery always goes up to over 13 volts after the solar panel is connected.
Mar 14, 2005
As with any piece of technology purchased new, if you are uncertain of how to use it, the first thing to do is to consult the supplied instructions, or ask the seller, especially as this one is selling several of the units they must be a business.

Without knowing the internal circuit diagram of the charger I could not be certain if your arrangement of linking the battery negatives is the cause of your discrepancy or not, BUT, as the pictograms on the unit shows the two batteries as separate items, and the two negatives are not adjacent to each other leads me to suspect the batteries should have individual wires to their terminals.

As you also have two types of battery connected, and we don't know if the batteries are different ages, one of them could be unsatisfactory condition.

I'm sure the instruction that came with the unit should tell you how to wire the controller, or if not you should be able ask the seller as they seem to be selling several of them they must be a dealer.
Oct 8, 2006
This is the type fitted to Bailey Unicorns, and indeed it does require separate wiring from the two batteries.

Also it is necessary to make sure the controller 'knows' which type of battery is being used in both positions. My ordinary Varta wet lead acid leisure battery is type 391.


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