How To Calculate The Battery That I Need For A 50 L Fridge ?

Deciding what size battery is required to power a portable fridge for your next camping holiday can be challenging.

There is a few factors to consider like how much power does a fridge need but also would you have access to a charging point during your time away.

A charging point could be solar panel or access to a main power point if your fridge is connectable.

Other alternative is to have a Dual battery switch isolator or a DC to DC charger in which case you will be able to use your car alternator and not discharge your car cranking battery.

Fridges should never run off the cranking battery.

We found it easier to calculate with Amp and hours than W/h as more often battery are in A/h.

You need to know 3 things:

• The Amperage that your Fridge draws when running
• How long it will be running
• The size of the battery in Ah that you want to use

Most portable fridge will consume between 2 amp and 5 amps (with 2.5 amps being the average) an hour when running.

In reality the fridge compressor will only run-on average 30% of the time.

Using the example below, where the fridge draws 2.5 amps when the compressor is on but only runs for 1/2 the day.

Example of calculation:

2.5A X 12h= 30 Amp/h

it will use 30 Amp hours of the battery capacity in 24 Hours.

With a 120Ah Battery you should only use 50% of the battery before recharging as a rule to keep your battery in good condition, so you have 60 Amp available.

With 30 Amp consumption and 60 Amp available to use you will be able to power your fridge for 48 hours.

If planned correctly and considering ambient temperature, insulation thickness, the temperature they are set to cool to, how often you are using it for, and how full they are a 120 Ah battery should be enough for a week end away.

What battery should a fridge run off?

The best design battery to use for powering a fridge is a deep-cycle battery, which is designed (as the name suggests) to cycle from full to half empty and charge again.

Cranking battery are not design to be cycled and you will shorten their life substantially. Lithium batteries are also becoming more popular as they have several advantages, but they are still pricey.

How to know when a battery is down 50%?

Your battery will below 50% of charge, when it’s down around 12.2 – 12.3 volts.

An other way to measure is to install small capacity gauge.

 Also most fridges have a low-level cut-out, but it’s not usually until well under 12 volts. If you run your battery below 50% of charge, its lifespan will rapidly be decreased, and batteries aren’t cheap.

Also if you want to add more electrical accessories you can apply the same formula consumption Amperage X time being used = Ah.

You can then substract to your battery capacity.

You might use:

• Lights consumptions 2 Amp 2 hours a day = 4 A/h
• TV consumptions 5 Amp 2 hours a day = 10 A/h
• Water pump consumptions 3Amp 1 hours a day = 3A/h

 Total power that would be used bu these 3 items = 17A/h

When choosing a 50L Portable fridge you should consider it’s efficiency.

How much is the A/h consumption and verify the manufacturer specifications by doing the calculation.  

Finally how good is the insulation in other word how often will the compressor be running.

Alternative for Deep cycle battery are Power center that run on lithium batteries which are becoming more efficient and are rechargeable with solar.

If going away for a week you might want to consider Lithium batteries and Dual battery system to rechage.

Lithium Batteries have many benefits:

• The full Amp Hour capacity of a quality lithium battery can be used without effecting the life span of the battery (a lithium battery rated at 100 amp-hours is closely comparable to 200 amp-hours of AGM or lead acid batteries in terms of usable power.)
• Lithium batteries also maintain a higher output voltage during the discharge cycle 
• Your accessories, camp lights or fridges will they run more efficiently and with a longer run time
• Lithium batteries also charge significantly faster than an AGM/lead acid battery.
• Lithium is that they are considerably lighter than a similar sized AGM or lead acid battery