Ampere Hours Ah

[Jim]

An Ampere Hour (Ah) is a way of measuring how much electricity a battery can store and provide over time. It’s especially important for motorhomers using leisure batteries because it helps you understand how long your battery will last before needing a recharge.

Breaking it Down Simply:​

• 1 Ampere (A) is the amount of electrical current flowing.
• 1 Hour is the time it flows for.
• Ampere Hour (Ah) is a combination of the two.

For example:

• A 100Ah battery can, in theory, supply 100 Amps for 1 hour or 10 Amps for 10 hours or 5 Amps for 20 hours before it runs out (though real-world conditions affect this).

Why It Matters for Motorhomers:​

1. Estimating Power Use – If you have a device that uses 5 Amps (e.g., a 12V TV), a 100Ah battery could power it for roughly 20 hours before running out.
2. Understanding Battery Limits – Many leisure batteries shouldn’t be fully drained. A lead-acid battery should ideally not go below 50%, meaning a 100Ah battery really only gives you 50Ah of usable power. A LiFePO4 battery can be discharged much further.
3. Choosing the Right Size Battery – If you run a fridge (5A), lights (2A), and a heater fan (3A), using 10A per hour, a 100Ah battery will last around 5 hours before hitting 50% capacity.

Key Takeaways:​

• Bigger Ah = More stored energy = Longer running time.
• Usable Ah depends on battery type (lead-acid vs lithium).
• Know what you use to avoid running out of power!

 

[funflair]

It’s also worth remembering that a 24v 100ah battery stores twice the power of a 12v one, the ultimate expression of power is watts and watts/hour watts = voltsxamps so the battery above is 2400 or 1200 watt hours now by using the wattage of the TV or fridge you can easily see how long you can run a piece of electrical equipment, you can even combine watts at 12v or 240v. But yes we seem obsessed with ah and make life more difficult

Post edited watts to watt hours

 

[Carpmart]

As long as we all talk the same technobabble and it’s relatively easily interpreted by all, once the basics are understood, it doesn’t really matter what units we use…

 

[Jabstatt]

Hoorah!

Let’s get amp hours sorted once and for all.

Good job Jim.

It isn’t difficult.

Tony

 

[Jabstatt]

It’s also worth remembering that a 24v 100ah battery stores twice the power of a 12v one, the ultimate expression of power is watts and watts/hour watts = voltsxamps so the battery above is 2400 or 1200 watts now by using the wattage of the TV or fridge you can easily see how long you can run a piece of electrical equipment, you can even combine watts at 12v or 240v. But yes we seem obsessed with ah and make life more difficult

No it’s not!

It’s 2400 watt hours. Amp hours is very straightforward. And most of our systems are 12v and we learnt our twelve times tables.

Tony

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[meanders]

The other key factors are space and weight when it comes to batteries. Generally speaking the bigger Ah batteries take more space and payload. A Lithium is roughly half the weight of a lead acid and substantially smaller in size like for like power wise.

 

[funflair]

No it’s not!

It’s 2400 watt hours. Amp hours is very straightforward. And most of our systems are 12v and we learnt our twelve times tables.

Tony

Indeed guilty as charged I will edit my post to save even more confusion.

 

[Jabstatt]

Thanks!

Tony

 

[meanders]

No it’s not!

It’s 2400 watt hours. Amp hours is very straightforward. And most of our systems are 12v and we learnt our twelve times tables.

Tony

Sorry but funflair Martin is correct that Watt/hr is more important than amp hours. Indeed it becomes important in the calculations as the battery voltage fluctuates. However, for the majority of uses, Ah is sufficient and as batteries are sold by that rating, it's simpler.

He is also 100% correct that two 12v batteries in series delivers a nominal 24v and doubles the overall power.

However, as every appliance has a rating in watts so if talking in Ah you have to know how to convert to Amps at any given voltage. Maybe if we could persuade all battery suppliers to convert to Wh, it would help with all the questions of can how long can I run my 3000W heater from my 80Ah battery.

Edit. I see everything has changed since I started typing.

 

[Pausim]

My Roamer Li is 230Ah and weighs 22kg. It replaced 160Ah of Gel batteries weighing 56kg, significantly less than half the weight and significantly more stored power.

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[Steve and Denise]

As long as we all talk the same technobabble and it’s relatively easily interpreted by all, once the basics are understood, it doesn’t really matter what units we use…

You tell them H Let’s re-write the book
Is the fridge all installed and working now ?

 

[dunnah01]

I've now got a headache from reading this, could you give it a few days before posting the next episode 'How to Charge your Leisure Batteries'

 

[KNWH]

I thought an Ah was just the noise I make when I sit down. Or stand up.

 

[Jim]

This thread was created as a link for the keyword "Ah" I set the date to a year ago so you'd not see it, but some of you are too quick.

Keywords are the linked words that appear in posts and link to an explanation for newbies. . However, feel free to continue the discussion

 

[Rapido925M]

He is also 100% correct that two 12v batteries in series delivers a nominal 24v

Why would anyone join 2 x 12V batteries in series to provide 24V when (all?) our low voltage appliances work on 12V?
Join them in PARALLEL!

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[Jabstatt]

Really?
24v inverters and many items such as water pumps are available in 24v often popular in the marine industry as well.
Lighter cabling, half the current and great to have solar at 24v, lightweight wires again.

Tony

 

[Rapido925M]

I thought this was related to MOTORHOMES. I’m sure those interested in boats, lorries etc have their own forums
Sadly, some people don’t understand electricity and a comment about the advantages of wiring batteries in series might just encourage them to do that

 

[meanders]

I think you will find funflair and others drive machines that have 24v electrics by default. It makes no sense to have 12 and 24v systems side by side. My joined in series wasn't a instruction but a statement of the reality on a 24v battery having double the number of cells. I was not suggesting people do it in a 12v van.

However, your reply does highlight it to anyone who reads this and is not understanding.

 

[Jabstatt]

I think you will find that a lot of larger RV type vehicles run on 24v.
Great where more power is needed and it’s standard for starting larger diesel engines.

Tony

 

[Minxy]

I've now got a headache from reading this, could you give it a few days before posting the next episode 'How to Charge your Leisure Batteries'

You're not the only one!

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[Carpmart]

You tell them H Let’s re-write the book
Is the fridge all installed and working now ?

Steve and Denise Not arrived yet Steve, at local delivery depot so expecting it anytime soon, probably tomorrow! Old fridge is out and think I’ve found a recycling centre to drop it off at… holding off as a local bloke wants to potentially buy it to harvest parts.

Do you recall clearances when you fitted yours Steve? Is the fridge completely flat backed so needs 563mm clearance top to bottom? I’ve got quite a large wiring loom/harness and an Alde pipe run round the back of the fridge space, all low level, but may need some fettling!

 

[bigtwin]

Why would anyone join 2 x 12V batteries in series to provide 24V when (all?) our low voltage appliances work on 12V?
Join them in PARALLEL!

There is no one universal approach! You are making a big assumption about others’ systems.

There are very good reasons (e.g. cost, weight, etc) why one might put two 12V batteries in series. Perhaps you’re not aware of them.

Ian

 

[bigtwin]

Sadly, some people don’t understand electricity and a comment about the advantages of wiring batteries in series might just encourage them to do that

So it seems!

The use of 24V systems isn’t the preserve of boats and lorries it’s just that 12V is the most common in MH circles.

Ian

 

[meanders]

I remember an old Dormobile or the like many years back that had 6v Electrics as did many cars and bikes. I also helped a mate convert his car from 6V to 12v with new dynamo, starter motor and many bulbs. If my memory serves me correctly it was a Ford E93A.

 

[B+W vanman]

I remember an old Dormobile or the like many years back that had 6v Electrics as did many cars and bikes. I also helped a mate convert his car from 6V to 12v with new dynamo, starter motor and many bulbs. If my memory serves me correctly it was a Ford E93A.

Yes, the Ford Anglia/Popular “sit up and beg”!
The 6v was useless in the winter, mind you, having dynamos, not alternators, didn’t help

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[meanders]

The thing I remember most is that the semaphore indicators did not like 12v so we put a large wirewound resister in series to drop the voltage back but that caused a problem with heat. He bit the bullet and bought a flashing indicator kit that was supposed to just fit... Ha Ha. I don't remember the why, but we had lots of issues fitting a supposed 'kit'.

 

[funflair]

I think you will find funflair and others drive machines that have 24v electrics by default. It makes no sense to have 12 and 24v systems side by side. My joined in series wasn't a instruction but a statement of the reality on a 24v battery having double the number of cells. I was not suggesting people do it in a 12v van.

However, your reply does highlight it to anyone who reads this and is not understanding.

Ours is actually a 12v chassis but the mainstream manufacturers of big vans on 24v chassis actually still use 12v for the habitation batteries so they have to have a second alternator at 12v or a step down B2B, yes the Motorhome habitation is 12v but is actually low wattage so uses few amps anyway, it’s the higher wattage equipment supplied via an inverter at 240v that would benefit from a 24v or even 48v feed so then the power cables could be much smaller to carry the reduced amps remembering that watts=voltsxamps so amps=watt/volts so the amps go down as the volts go up and consequently cable sizes come down or get more efficient which would benefit solar and higher voltages.

 

[Minxy]

My head is just about to burst!

 

[bigtwin]

My head is just about to burst!

Watt are you talking about?

Ian

 

[meanders]

My head is just about to burst!

If you have a "standard' motorhome it will be 12v throughout. We are talking exceptions not the norm.

Assuming that's the case, then generally the bigger the battery, the longer it will run the equipment you have without charging. Moving to Lithium saves a lot of weight and will give you more power for longer but you need a suitable charger and solar controller.

If putting in an extra battery or more, you connect all the + terminals together and all the - terminals together so still delivering 12V but double, treble or more the capacity. However, the batteries all need to be the same size, type and age. I.e buy them and fit at the same time.

Hopefully a little clearer.

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