I have an appliance that needs to run for around 10 hours, even if there's a power cut. I don't need a UPS, as I'll just connect the appliance to a battery if needed.The appliance uses around 50w of electricity, and it happily runs off 12v. So, a 40Ah car battery seems at first glance like it will do, except it won't survive being discharged down to nothing too well.The standard solution is a leisure battery, although these are very expensive. Could I use two standard car batteries (in parallel) instead? Are they okay with being discharged 50%?

An 80Ahr leisure battery should do it - you should discharge even a leisurebattery below 50% if you want long life. A decent one will cost about £70or so from Tanya. I like Hankook batteries with a 4 year warranty. Ideallya smart charger but a simple float charger at worst. Don’t cook it byleaving it on charge at too high a voltage too long.

On 09/09/2022 00:53, Fredxx wrote:

Leisure battery needed?

Sep 05, 2022 Last reply: 3 years ago 25 Replies

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Harry Bloomfield Esq 3 years ago

I use leisure batteries in my tourer caravan for decades, which have

13.8v regulated as the charging supply. The caravan is parked up in my drive and I would just leave it powered on mains, to keep the battery charged. I have twice had sealed batteries fail, in just a few years, maintained on that 13.8v supply. Basically, the batteries had dried out.

Since then and changing my regime to just giving them a boost every one or two months, my present battery has lasted 10 years and my battery tester suggests it has 90% of it's original capacity.

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Fredxx 3 years ago

I have read that 13.0V is considered a maintenance charge. A gel VRLA should have a catalyst to return any gases back to water. I guess some are better than others.

I have a starter battery that is 9 years old and still holds a good charge. If treated well and never discharged to less than 50%

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Fredxx 3 years ago

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Animal 3 years ago

Batteries with catalyst are a big extra cost, and seldom worth it

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Martin Brown 3 years ago

That is a terrible thing to do to a lead acid battery.

Using 13.8v is *instead* of the battery is fine but applying 13.8v continuously to the battery will have the effect that you describe.

You would probably get away with it if there was a silicon diode in series with the 13.8v regulated supply to drop 0.6v.

Never a good idea to overcharge or totally discharge batteries - it shortens their working lifetime.

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Fredxx 3 years ago

This article gives a good overview:

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