Content of the material
Problems with rechargeable batteries
Manufacturers now claim that you’ll get hundreds of recharges from their batteries. The longest claim I’ve come across is the five-year lifetime guarantee or three hundred recharges (whichever comes sooner) for Duracell’s Recharge Ultra batteries.
But even with so many potential repeat uses, more than four in 10 of the Which? members we asked had problems with theirs in the past year alone.
Older batteries lasting less time between charges than newer ones, difficulties in charging them and batteries not lasting as long as expected on one use were among the most common problems.
So if you’re looking to buy new batteries. what should you look for? Our tests have found that the best rechargeables strike a balance between long battery life on a single charge and reasonably fast recharging. Plus, they don’t leak away charge when not in use.
Oh and that tip about sticking the batteries in the fridge? Our sister publication in the US, Consumer Reports, has tried this with disposables but sadly found it made minimal difference to battery life.
When your room’s temperature isn’t “room temperature”
While refrigeration is a no-no, temperature still has a big impact on a battery’s shelf life.
When battery makers recommend “room temperature,” they generally mean between 68-78°F. Depending on your location, though, your house may get a lot warmer than that. And the hotter it gets, the faster your batteries lose their charge. Stored in a hot garage or closet, those batteries could drain themselves out two- to four-times faster.
Lithium likes it cool
However, research into lithium ion batteries (introduced in the 1990s and rapidly replacing Alkaline in many applications) found that they, like Zinc-carbon, did also benefit from cold storage. Their self-discharge could be reduced from 4% per month to 2% per month if stored close to 32°F (0°C).
How many batteries are needed to run a 12V fridge/freezer?
You can use 1 pc 12V 100Ah AGM battery, or 2 pcs 50Ah batteries to run your 12V fridge for approximately 20-40 hours depending on your fridge’s actual power consumption.
If you need your fridge to run for say 10 hours, you can use a smaller size battery.
1 pc 12V 50Ah AGM battery can power your 12V fridge for about 10 – 20 hours.
In addition to the actual power consumption, the number of batteries you need to power your fridge depends on how long you plan to run your fridge each day.
For example, you can double your fridge’s run-time to about 40-80 hours, by connecting it to 2 pcs of 100Ah battery in parallel or 4 pieces of 50Ah battery AGM battery.
Note: The above runtime estimates assumea fridge or freezer with daily consumption of less than 1kWh (<90W)
Electrical setup for powering a 12V fridge on batteries
The battery is only part of the electrical setup you need to run your 12V fridge reliably.
To provide your fridge/freezer with electricity you can use the car’s electrical system, a solar system, or grid power (Yes, some fridges can be powered by both 12V and 110V!)
Using your car’s electrical system
You can power small 12V fridges (65 -90W) using the car’s electrical system by plugging them into the cigarette lighter.
Beware though that the fridge can drain your car’s battery.
To prevent your battery from running flat, keep your car’s engine is running when the fridge is plugged in.
Note: Some portable fridges/freezers have a low voltage disconnect or battery saver system that switches of the battery when its voltage is getting dangerously low to prevent your car’s battery from being drained flat.
Make sure this feature is activated.
An example of a solar system set up to power your 12V fridge with consumption of under 1kWh per day and powers your fridge for about 10 hours
- 50Ah AGM battery
- 100W solar panel
- 20-30A charge controller
or a 105W solar panel only in case the fridge/freezer has a 50Ah AGM or 15Ah Lithium inbuilt battery
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Deep-Cycle vs Starter Batteries and Your Car Fridge
Pretty much all cars have a “starter” or “cranking” battery. This is the one that delivers the power to turn your engine over until it fires up. On those cold mornings when your engine won’t start and you hear that “RehRehRehRehReh” while you sit there saying “C’mon! C’mon! C’mon! Start damn-it”. That’s all on battery power. Do it too long and pretty quickly your cranking battery runs out. Starting your car requires a burst of 100 to 200 amps. And 300 amps isn’t unheard of. Your cranking battery is designed to deliver it for a short period of time.
Which is why running your car fridge off your cranking battery isn’t the best idea. The same applies for anything that you use for a long time while your car isn’t running (camp lights for example). If you over-discharge your cranking battery more than a few time then it rapidly stops being able to hold a charge at all. Cranking batteries can’t be discharged more than about 25% before their lifespan is depleted.
Your typical deep cycle battery, however, is designed to store energy and deliver it at lower amperages for longer periods of time. Most can be discharged to 50% of their capacity before their life is compromised. And some of the best ADM or Lead Acid batteries can be run down to 75% of their maximum charge without damage. So these are the guys you want to be using to power your car fridges, camp lights etc. You might think of deep cycle batteries as marathon runners, and cranking batteries as sprinters.
What to, and what not to, chill
So here’s the definitive guide:
- If the battery is zinc-carbon (including zinc-chloride) or lithium based, its self discharge rate can be reduced if kept refrigerated.
- Your fridge needs to be a dry environment (some older fridges can be damp), or the battery casing or terminals may rust causing toxic leaks that you really don’t want near your food.
- Do not use a battery straight from the fridge, allow it to warm up gradually to room temperature (a few hours is needed for a unit to warm right through).
- Don’t try to accelerate this warming process (say by putting it beside a sunny window), as this will cause the outer parts of the battery to become too hot and excessive heat accelerates self-discharge.
- While the battery is warming up, keep it in a well ventilated area to avoid condensation which could cause shorts or rusting.
- For everyday usage, don’t get too hung up on it. The benefits are very small unless you are talking about commercial storage to extend shelf life.