An effective battery set up on a narrowboat is crucial as this is the main energy source. The energy taken out of the narrow boat battery bank needs to be replaced ….. one thing is sure, you will need to put back a little more than you took out!

A battery charging set up on a narrowboat is crucial to ensure you have power when needed
Narrowboat batteries have a maximum charging life cycle
Understanding how to charge your narrowboat batteries is crucial

Charging… The Basics!

Narrowboat battery technology can be very complicated, so we will explain the process here in very basic terms. There are some very good resources available the public domain for those who wish to take their understanding to the next level.

It may seem obvious, but it’s important to remember to we need to put back into the narrow boat battery any energy we use.

As we have seen in the Battery section, lead-acid batteries can be discharged to different states of discharge depending upon their type. Whether that be the starter bank, the leisure system or an auxiliary bank, such as the bow thruster, in order for us to have the power we require on hand that charge should be put back in as soon as possible.

Our fully charged lead acid battery cell sits at around 2.1 volts. Remember the batteries we are used to are multiple cells, usually six to a case. So for familiarity we will refer to a fully charged battery voltage being 12.6 volts

Easy, you’d think all we need to do is to put our amps back in at 12.6 volts and everything will be OK. Not so, as battery voltage rises, so does the resistance. Therefore we effectively have to charge at a higher rate to force the battery back to a full state of charge.

So why not just use a constant higher voltage, such as 14 volts for example to recharge the battery? Well that’s what older battery chargers and basic dynamos on vehicles used to do. Many years ago, however there wasn’t the technology available to the general market for living off batteries like we now do. As our demands have increased, so has technology. We now require maximum potential at minimum cost and this is reflected in battery charging technology.

By just putting an unregulated, constant voltage into the battery we would not get the value from the unit we require. So, why is that? Well, this is where it can get complicated so you will have to trust us when we say that the correct charge voltage is critical. Too little and the battery life will be shortened. Too much and guess what!

  • Charge voltages range from 13.8 to 14.4.
  • The balance is one between maximum service life, maintenance and ease of use.
  • Charging at a constant 13.8 volts would give maximum service life and the battery would remain cool. The flip side is that charge ties are slow (we need that power now!), battery capacity will gradually decline and sulphation may occur.
  • Charging at 14.4 volts would charge the bank faster, the capacity would be more consistent and there will be less sulphation. However, at this voltage there will be the production of volatile gas, the battery would need constantly topping up and over time there would be a severe overcharge.

So now we can see why it can be complicated getting the balance right. Fortunately technology has given us the intelligent multi-stage battery charger. If you haven’t got one on your battery banks yet, hopefully the above has convinced you that it would be an investment worth making.

Three Stage Charging

Three stage charging is best described as bulk, equalisation and float. There are chargers that promise more stages but we will keep it simple.

  • Bulk Stage

The bulk charge basically fast charges the battery close to full capacity. It regulates the voltage in order to rapidly replace lost amps whilst minimising heat build-up and gassing. It applies constant current at increasing voltage as the resistance to charging increases.

  • Equalisation – Absorption Stage

After a regulated period of time depending upon state of discharge, original battery capacity and the rating of the charger unit itself, the charger will switch to the equalisation phase. Once the voltage peaks, the charger decreases the current. It holds the peak voltage and forces the battery to accept the last few amps of it’s capacity by dropping the current.

If you can imagine eating a box of chocolates. By stuffing them all in at once you will feel fuller quicker but may be ill, forcing you to stop. A little later you may have extra capacity. By eating them slowly, one at a time you could manage a lot more before you felt ill and full!

  • Float Stage

The final stage of charging is known as the float stage. This stage lowers both current and voltage to maintain the optimum capacity of the battery and to compensate for any natural self-discharge.

There are a number of different methods available to us to put charge back into the narrow boat battery banks.

If you are buying a narrowboat sailaway or re-fitting a canal boat you will need to consider what type of charging system is most suitable depending on how you will be using your narrow boat, for example, will your canal boat be a live aboard or for leisure use? Will you have shoreline power? If you are purchasing a new build narrowboat, consult your canal boat builder for the charging specification included your purchase and any upgrades that may be available.

Charging Set Ups

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crick boat show 2024

(Saturday 25 to Monday 27 May 2024)


Britain's biggest inland waterways show.

Advance tickets can be ordered by phone and online until 12midday on Friday 17 May 2024. If you are planning to purchase advance tickets, we recommend that you do so well before this deadline to allow time for postal delivery.
Children 16 and under – free entry Saturday, Sunday, Monday

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Get ahead and visit The Fit Out Pontoon before everyone else on Preview Day!
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