Job of the day: Charging narrowboat batteries in series

Job of the day: Charging narrowboat batteries in series

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Now I’ve been told this can be done.

There’s no reason you can’t charge batteries in series,

Charging a narrowboat batey in series.
Charging a narrowboat battey in series.


As the diagram suggests, you need a 24V charger to make an adequate PD or potential difference across the two batteries in order that they accept charge.

I don’t have a 24V charger, I have a 12V charger, or 17.2V charger when on quick-charge.

This won’t be enough that the batteries actually charge, and I’m finding this when I disconnect the charger.

Starting the engine and running it is the only way to charge the batteries.

However, I’m not seeking to charge the batteries.

Shoreline RR47 12V fridge

Shoreline RR47 fridge
Shoreline RR47 fridge

What I’d like them to do is fire up the compressor on my RR47 shoreline fridge. The fridge is the important part, not the charging of batteries.

In that sense, the title may be a bit misleading. The title should be, firing up the compressor on my Shoreline RR47 12V fridge, but that sounds a little boring.

In order that the compressor fires and my food gets cooled, it requires a PD of around mid 12’s. Anything below 12.4V and the fridge simply doesn’t fire up.

The manual claims that the fridge will be operational at 10V. This is simply not true.

From experience, the fridge will stop working when the voltage drops below 12.4V.

All I’ve done is run a wire to the battery compartment with some 3a wire, and connected it with 6mm rings to the terminals of the battery, IN SERIES.

Now, I no longer have to get up and run the boat rain or shine when the fridge goes off, I can simply plug the charger in, and hey presto, working fridge.

I’ve done a short video here.

In the course of time, the boat will be fitted with 240V and inverters.


4 thoughts on “Job of the day: Charging narrowboat batteries in series

  1. Good to see that you’ve cracked the fridge problem – and that there’s no need for vast outlay on replacement after all. I guess that previous Bonny owners only used it when out & about, when the engine running would do the charging.

    On another front, have a look at this free piece of software – it’s really quite good, as a freebie.

  2. Hello. I have 4 batteries placed into a series creating a 48v system; that is fed to my invertor (48v / 3000kw Victron)!

    The problem I have is that the alternator is only 12v 130amp (Canaline 42 / 2019).

    Can I charge my batteries on the 48v series by attaching the 12v alternator (albeit a slower charge rate) or will this blow the alternator? I am really struggling to get help on this.


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