accupower D battery compared to SLA

[detonateme]

ok...i know this will sound completely stupid to you techno savvy folks out there but i need some assist. I have one of those 15mil candle power cyclops thor spot lights and i want to upgrade my battery pack. the SLA battery in there now is 12v and 7ah in capacity. I found a site selling accupower d sized batteries which have a capacity of 11000 mah (10.1ah). how in the world could a little d siezed battery hold more juice than something 8 times its size?? If i wanted to chain 8 of these bad boys together for a new powerpak would it work? my only wonders would be on the voltage and charging the pak inside the spotlight. Can anyone offer a little assist here? thanks if so.

 

[Empath]

7X12 (84) is more than 11X1.25 (13.75)

 

[Mr Happy]

Since an NiMH has a nominal discharge voltage of 1.2 V you would need ten of them in series to be equivalent to a 12 V SLA. Question 1: would ten D cells fit in the same space as your 7 Ah SLA? Question 2: is the cost of ten D size NiMH plus necessary charger economical compared to the SLA?

For charging, you would need one of the hobby chargers that could do ten cells in a pack. Such a charger is unlikely to come in under $150.

 

[detonateme]

ohhh....see i looked all over the web on converting mah to ah and nothing was mentioned about it being per volt. sheeesh, now i understand. I would need far fewer NIMH cells if their voltage were much higher even if they were to stay at the same mah level. Thanks for clearing all that up. I think i will tear into a couple laptop batteries instead of using battery packs.

 

[lctorana]

7X12 (84) is more than 11X1.25 (13.75)

But 7X12 (84) is less than 11X1.25x8 (110)

And more to the point, you can repeatedly discharge that 110Wh much more deeply than the SLA. Flatten an SLA and it doesn't come back to full capacity. Smart advice says go for about 20% DoD for maximum battery life.

So 7 x 12.6 x 20% = 17.64 Wh for reliable long-term use.

But 11 x 1.2 x (say 75%) = 79.2 Wh - a massive improvement.

And 8 cells should indeed fit in the space. You need a different charging circuit, of course (constant 1.1A current rather than 13.8V constant voltage).

Only real disadvantage is the price. Ask yourself the hard question:
"Are these batteries worth more than the torch?".