## How long will this batt last? (consumption)

Hi, i 'm new here. (I 'm from Panama city, Panama).
I know very, very little from electricity and those stuffes. I hope you can help me out.

If I have a battery, say: 12v / 7ah

How long will it last (in ideal scenario), if I power a device that is: (one at the time).

1. 7 amp
2. 3.5 amp
3. 35 amp
4. 70 amp

Also, why do people say, that when you charge any rechargable battery, it should be from 10 to maximum 15% of its total ah?? However my cellphone (NOKIA N8) is: Standard battery, Li-Ion 1200 mAh (1.2ah) (BL-4D) and it's charged (from full discharge) in exactly 1 hour and 45 mins = 105 mins? that means that: 11.43 ma get in per minute, and 685.71 ma per hour (about 57.14% per hour). Why that exception???

So, can I charge a car 50ah battery in 30 minutes by charging it with 100amp???
50/100=0.5hours

Thanks
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 Thanks for answering Crosstalk, I think I should slap you in your face really hard, for suggesting I wanted you to answer my "homework". And yes, it's a homework, but for me. Since I want to get into solar panels stuff. In some other forum I asked some "experts", if by any combination or mix (paralell or series), could you manage to turn on and keep for 10 seconds a small a/c with "n" number of 1.5v batteries @ 1200 mah? They called me crazy, hehehe, but, in theory, is it possible? a/c = 700w @ 220v For 220v = 147 1.5v batteries. For 3.18amp (700w / 220v = 3.18 amp) = about 3 1.5v @ 1200mah batteries. Is it theorically possible with my combinations?

## How long will this batt last? (consumption)

 Quote by Panamanian Thanks for answering Crosstalk, I think I should slap you in your face really hard, for suggesting I wanted you to answer my "homework". And yes, it's a homework, but for me. Since I want to get into solar panels stuff.
Okay that makes sense -- and I asked because I'd rather not directly answer a homework question for anyone (plus it's against forum rules).

 In some other forum I asked some "experts", if by any combination or mix (paralell or series), could you manage to turn on and keep for 10 seconds a small a/c with "n" number of 1.5v batteries @ 1200 mah? They called me crazy, hehehe, but, in theory, is it possible? a/c = 700w @ 220v For 220v = 147 1.5v batteries. For 3.18amp (700w / 220v = 3.18 amp) = about 3 1.5v @ 1200mah batteries. Is it theorically possible with my combinations?
You mention a 220v air conditioner. Most home appliances run on AC current (alternating current). Batteries produce DC current (which doesn't alternate). Unless this air conditioner is able to run on DC current, then you cannot simply power it off of AA batteries.

Just for your information, the name for a device that converts DC into AC is an "inverter" -- so if you can find an inverter with the right specs then you could run the a/c through that inverter (as opposed to directly off of the batteries).

If this air conditioner runs on DC, however, then it's theoretically possible. If those batteries were actually putting out 1.5 volts, then your calculation of 147 batteries is correct. However, battery voltages actually sag under load. This drop in voltage can be compensated for -- if you know about resistance, then look up "internal resistance".

Your calculation for current however isn't quite accurate. That 1200mAh rating is capacity -- that calculation shows that you would need three strings of batteries, each putting out 220 volts, in parallel to get 1 hour of battery life. The number of these 220v strings you would need depends on the current-sourcing abilities of AA batteries, which I am less familiar with.

Also, in practice, batteries in parallel have a tendency to try to reverse-charge each other. I don't have enough experience or knowledge to comment on whether or not this would be an issue, however.
 The behavior of battery chemistries varies thr charging method. You should also consider the application of the battery. This site may help: http://batteryuniversity.com/
 I have a load of 3kW. 2 Batteries in series - each of 12Vand 42Ah Solar panel - 450W - 12V charging batteries with MPPT. Calculation to be done on the basis of charging i.e. taking care that battery is charging at the time of discharging. I need the calculation of the total time i can run the load which charging and discharging the battery. Plz explain how to calculate.

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