Small battery capacity question

[skyflyer]

I have a 6v DC device (monitoring camera) powered by 4x1.5 AA batteries, but with an external plug for 6v supply

The AAs don’t last very long so I’ve been thinking about buying a small lead acid (or AGM) battery to connect to the external socket. (Mains power adapter is not an option)

But if I’ve understood this correctly, it seems like the Ah capacity of a fairly weighty 6v batter is little more than the 4 x AA rechargeables in the camera.
Typical AA capacity is between 1500 and 2300 mAh, so that’s 2.5 1.5- 2.5 2.3 Ah right?

Typical capacity for a 6v gel battery ( about 150 x 75 x 100mm) is about 2Ah

So on the face of it I’d be better off making up an external battery pack of a dozen rechargeable AA batteries rather than use the lead acid?

am I missing something here? I keep thinking I have misunderstood, especially when you consider that a lead acid battery maybe 5 times that volume has a capacity (12v) of around 40Ah! That would be 80Ah at 6v

 

[andsarkit]

Does it really need 6V or would it run off a 5V usb power bank? Lots available up to 20Ah.power bank

 

[Spirit (of Glenans)]

I have a 6v DC device (monitoring camera) powered by 4x1.5 AA batteries, but with an external plug for 6v supply

The AAs don’t last very long so I’ve been thinking about buying a small lead acid (or AGM) battery to connect to the external socket. (Mains power adapter is not an option)

But if I’ve understood this correctly, it seems like the Ah capacity of a fairly weighty 6v batter is little more than the 4 x AA rechargeables in the camera.
Typical AA capacity is between 1500 and 2300 mAh, so that’s 2.5 - 2.5 Ah right?

Typical capacity for a 6v gel battery ( about 150 x 75 x 100mm) is about 2Ah

So on the face of it I’d be better off making up an external battery pack of a dozen rechargeable AA batteries rather than use the lead acid?

am I missing something here? I keep thinking I have misunderstood, especially when you consider that a lead acid battery maybe 5 times that volume has a capacity (12v) of around 40Ah! That would be 80Ah at 6v

Batteries intended for motorcycles might fit the bill. Consider some of these:
VIPOW 6V 12Ah AGM GEL Battery Sealed Maintenance Free Backup Energy Supply : Amazon.co.uk: Automotive
YTX7L-BS / MG7HL-BSDefault Title
YUASA Batterie B39-6 Dry Charged (ohne Batteiresäure) 6V/7Ah | eBay
Batterie 6V - 12Ah - Vliesbatterie 0811, mit Deckel | eBay
Google Translate may be of assistance in evaluating the specs of the last one.

 

[PaulRainbow]

I have a 6v DC device (monitoring camera) powered by 4x1.5 AA batteries, but with an external plug for 6v supply

The AAs don’t last very long so I’ve been thinking about buying a small lead acid (or AGM) battery to connect to the external socket. (Mains power adapter is not an option)

But if I’ve understood this correctly, it seems like the Ah capacity of a fairly weighty 6v batter is little more than the 4 x AA rechargeables in the camera.
Typical AA capacity is between 1500 and 2300 mAh, so that’s 2.5 - 2.5 Ah right?

Typical capacity for a 6v gel battery ( about 150 x 75 x 100mm) is about 2Ah

So on the face of it I’d be better off making up an external battery pack of a dozen rechargeable AA batteries rather than use the lead acid?

am I missing something here? I keep thinking I have misunderstood, especially when you consider that a lead acid battery maybe 5 times that volume has a capacity (12v) of around 40Ah! That would be 80Ah at 6v

How about a DC-DC converter and run it from the main batteries ?

 

[BabaYaga]

Typical capacity for a 6v gel battery ( about 150 x 75 x 100mm) is about 2Ah

So on the face of it I’d be better off making up an external battery pack of a dozen rechargeable AA batteries rather than use the lead acid?

am I missing something here? I keep thinking I have misunderstood,

Not sure I quite follow your calculations, but a 6v gel battery of those dimensions should have something like 12 Ah capacity.
Also, Ah as a measurement of battery capacity always assumes a voltage, so when making comparisons between batteries of different nominal voltage (in this case 6 and 1.5 v) this must be taken into account. Best to convert to Wh.

 

[KompetentKrew]

I wonder if OP is conflating usable battery capacity with actual battery capacity.

The first two batteries in @Spirit (of Glenans) list of links are about the size that @skyflyer mentions, and are specified as 12ah and 7.5ah respectively.

But, as any fule kno, one cannot use the full capacity of lead acid or AGM batteries, as running them completely flat kills them. They have a useable capacity of about 20% to 50% of their nominal capacity, depending on how kindly you wish to treat them.

The energy density will not be that much difference between 12v and 6v batteries, AGM or flooded lead acid, or AA or AAA batteries - but you will get 2x or 5x the usable capacity out of disposable AA batteries because you run them until they're dead and then throw them away.

@PaulRainbow's suggestion to run a voltage converter resonates with me - presumably you have shore power or a solar panel, so everything is taken care of this way. I think you would place the voltage converter next to the device, if there's a long run of cable, as voltage loss will be lower over 12v than over 6v.

 

[Alex_Blackwood]

I have a 6v DC device (monitoring camera) powered by 4x1.5 AA batteries, but with an external plug for 6v supply

The AAs don’t last very long so I’ve been thinking about buying a small lead acid (or AGM) battery to connect to the external socket. (Mains power adapter is not an option)

But if I’ve understood this correctly, it seems like the Ah capacity of a fairly weighty 6v batter is little more than the 4 x AA rechargeables in the camera.
Typical AA capacity is between 1500 and 2300 mAh, so that’s 2.5 - 2.5 Ah right?

Typical capacity for a 6v gel battery ( about 150 x 75 x 100mm) is about 2Ah

So on the face of it I’d be better off making up an external battery pack of a dozen rechargeable AA batteries rather than use the lead acid?

am I missing something here? I keep thinking I have misunderstood, especially when you consider that a lead acid battery maybe 5 times that volume has a capacity (12v) of around 40Ah! That would be 80Ah at 6v

If the 6volt external connection will charge the rechargeable batteries in the camera (Some do some don't) why not just make up a small solar panel and connect to that.

 

[ean_p]

I have a 6v DC device (monitoring camera) powered by 4x1.5 AA batteries, but with an external plug for 6v supply

The AAs don’t last very long so I’ve been thinking about buying a small lead acid (or AGM) battery to connect to the external socket. (Mains power adapter is not an option)

But if I’ve understood this correctly, it seems like the Ah capacity of a fairly weighty 6v batter is little more than the 4 x AA rechargeables in the camera.
Typical AA capacity is between 1500 and 2300 mAh, so that’s 2.5 - 2.5 Ah right?

Typical capacity for a 6v gel battery ( about 150 x 75 x 100mm) is about 2Ah

So on the face of it I’d be better off making up an external battery pack of a dozen rechargeable AA batteries rather than use the lead acid?

am I missing something here? I keep thinking I have misunderstood, especially when you consider that a lead acid battery maybe 5 times that volume has a capacity (12v) of around 40Ah! That would be 80Ah at 6v

I think were your going wrong is that of the four batteries the voltage is accumulated in this case and not the amperage. Therefore you have 6v with 1500- 2300mAh and not 6v and 2Ah. So your lead acid battery would have around ten times the capacity if I understand your situation right.

 

[skyflyer]

Sorry, should have given more info! I plan to use this on and off the boat; as others have suggested, its easy on the boat with a buck converter powered by main batteries.

Off the boat that's not an option. The batteries within the camera do not charge when the external power is connected.

Regarding voltage differences - the 4 x AA are connected in series to make 6v, so the capacity of an individual battery is the capacity of the entire bank at 6v (if they were in parallel the entire bank would have the capacity of one battery x 4)

This battery is 4Ah 6v and dimensions are L: 70mm W: 47mm H: 105.5mm As has been said above, you wouldnt want to discharge below 50% so effectively its 2Ah usable capacity

In that volume you could fit 38 AA batteries, which in banks of 4 (to make 6v) call it 36 so thats 9 banks x 2.3 Ah = 20.7 Ah

In other words, led acid/gel/agm seem to be very inefficient capacity wise compared to NiMh (say) albeit that 36 NiMh AA will cost £50 or thereabouts .

 

[skyflyer]

Batteries intended for motorcycles might fit the bill. Consider some of these:
VIPOW 6V 12Ah AGM GEL Battery Sealed Maintenance Free Backup Energy Supply : Amazon.co.uk: Automotive
YTX7L-BS / MG7HL-BSDefault Title
YUASA Batterie B39-6 Dry Charged (ohne Batteiresäure) 6V/7Ah | eBay
Batterie 6V - 12Ah - Vliesbatterie 0811, mit Deckel | eBay
Google Translate may be of assistance in evaluating the specs of the last one.

Yes, I did eventually realise that you can always get a bigger battery, but portability is an issue and really my question was aimed at confirming my conclusion (ie that I am not making a schoolboy error) that lead-acid isnt a great chemistry in terms of 'capacity per cubic meter' let alone 'capacity per kilo'!

 

[skyflyer]

I think were your going wrong is that of the four batteries the voltage is accumulated in this case and not the amperage. Therefore you have 6v with 1500- 2300mAh and not 6v and 2Ah. So your lead acid battery would have around ten times the capacity if I understand your situation right.

Indeed - but 2000mAh is the same as 2Ah, is it not? (2000mA = 2 A)

 

[BabaYaga]

This battery is 4Ah 6v and dimensions are L: 70mm W: 47mm H: 105.5mm As has been said above, you wouldnt want to discharge below 50% so effectively its 2Ah usable capacity

The volume of that battery is only about one third of the battery dimensions given in post #1.
12/3=4.

 

[skyflyer]

The volume of that battery is only about one third of the battery dimensions given in post #1.
12/3=4.

Yes, sorry, agreed (i was estimating in post 1) but the argument in the later post stands. For a given space it seems you will get better capacity from a bank of AA rechargeables than lead acid. However I'm sure there are many other factors to consider (like maximum current draw, and maybe total lifespan, charge cycles etc)

 

[BabaYaga]

Yes, sorry, agreed (i was estimating in post 1) but the argument in the later post stands. For a given space it seems you will get better capacity from a bank of AA rechargeables than lead acid. However I'm sure there are many other factors to consider (like maximum current draw, and maybe total lifespan, charge cycles etc)

Remember rechargeable cells are only 1.2 v, so you would need 5 in series to get 6 v.
Also, I cannot see that you could stuff 38 or even 36 AA cells in the volume given in post #9.
I have in front of me a box of tightly packed AA cells (24 of them), so I would estimate the minimum dimensions to store 36 cells at 125 x 65 x 55 mm (with no allowance for trays, connections etc).
You may still have a point, though.

 

[ean_p]

Indeed - but 2000mAh is the same as 2Ah, is it not? (2000mA = 2 A)

Indeed you are right and I must have been having a brain f**t or something similar....!