# Battery life

#### brendyboy

Joined Dec 21, 2005
27
Hi there

Can someone tell me (and explain how to calculate).....

How quickly a 50watt appliance will drain a 12volt battery (4x1.5 AA batteries)
assuming its constantly draining supply.

Do I simply devide 50 by 12 to get the current and then compare it to the amp hours stated on the battery???

Thanks
Bren

#### JoeJester

Joined Apr 26, 2005
4,390

You will need to know the AH rating of the battery.

#### Iodem_Asakura

Joined Sep 14, 2004
140
Time = AmpHr / (Power / Voltage)

PD.: If you have a pack of 4 AAA Batteries of 1.5V, you only get 6 Volts not 12.

#### brendyboy

Joined Dec 21, 2005
27
My mistake, i meant 8

so if the batteries are rated at 1500mAh each... am I right in saying that you get 12amp hours (1500x8) ??

therefore the sum is 12/ (50/12) = 12/4 = 3 hours?

#### JoeJester

Joined Apr 26, 2005
4,390
Batteries connected in series will increase the total voltage, but the AH rating remains whatever the published value is. This assumes you use the same rating for each battery. Don't mix and match.

Batteries connected in parallel will have a voltage consistent with the rated voltage, but the capacity (Ampere-hours) will add. Again, don't mix and match.

Your eight batteries at 1500mAH will supply 12 V @ 1500 mAH, typically for 20 hours. The battery specifications are probably at the 20 hour rate. Aircraft battery specs are typically at the hourly rate ... it's best to review the specifications for your situation.

#### alva

Joined Dec 14, 2005
12
Originally posted by brendyboy@Jan 4 2006, 12:21 AM
Hi there

Can someone tell me (and explain how to calculate).....
How quickly a 50watt appliance will drain a 12volt battery (4x1.5 AA batteries)
assuming its constantly draining supply.

Do I simply devide 50 by 12 to get the current and then compare it to the amp hours stated on the battery???
Thanks
Bren
[post=12874]Quoted post[/post]​
A 50 watt appliance from a 12 V battery would draw 4.1+ amps; Power=VxA
50 watts= 12V x 4.1+ A
As mentioned above your eight AA batteries in series would still only be 1500mAH or 1.5AH capacity, so a 50 watt appliance if it worked at all would only run a very short time before the batteries would be depleted due to high current drain.
That's why AA batteries are only used for very low watt uses.
A 1500mAH capacity means theoretically the battery could run for an hour at 1500mA or 1.5A current, a 4 amp current won't happen with these batteries.