Power in a Battery = Mah x V?

[JEDI]

p = I x E

nimh rechargeable: 1.2v x 2000 mah = 2.4watts?
li-ion rechargeable : 3.7v x 1500 mah = 5.55w?

mah can be substituted for current?

 

[Cerebus451]

As the h (hours) implies, mah is current over time, so your multiplication is giving you watt-hours (energy), not watts. To get peak power from the battery you would need to find the peak current (in milliamps) that it can provide.

 

[JEDI]

As the h (hours) implies, mah is current over time, so your multiplication is giving you watt-hours (energy), not watts. To get peak power from the battery you would need to find the peak current (in milliamps) that it can provide.

so:
nimh rechargeable: 1.2v x 2000 mah = 2.4watt hrs
li-ion rechargeable : 3.7v x 1500 mah = 5.55watt hrs

any easy way to figure out peak current?

 

[disappoint]

so:
nimh rechargeable: 1.2v x 2000 mah = 2.4watt hrs
li-ion rechargeable : 3.7v x 1500 mah = 5.55watt hrs

any easy way to figure out peak current?

https://electronics.stackexchange.c...t-a-aa-battery-can-deliver-for-a-short-period

 

[NutBucket]

What application are you dealing with? When peak current is involved, it is important to note that different chemistries are better suited to different current demands.

 

[JEDI]

What application are you dealing with? When peak current is involved, it is important to note that different chemistries are better suited to different current demands.

none.

just saw li-ion batteries with lower mah ratings that nimh batteries.
then I thought whats the point of buying the more expensive li-ion rechargeables?

then thought of ohms law but how to figure out current of the battery?

anyway, the gist is that li-ion has more power even if lower mah rating due to higher voltage.

 

[NutBucket]

The real key is energy density.

 

[Red Squirrel]

Technically yes, by multiplying voltage by amps you'll get watt hours. But not 100% right, as the voltage starts off higher then tapers down as battery depletes. Also, the actual amp hour of a battery changes based on the load. For example, a 100ah battery with a 1 amp load may actually give you more than 100ah, while the same battery might only give you like 50ah with a really big heavy load. When they rate batteries they usually rate them for a certain amount of hours, like "100ah at 20 hours". Because of this it's often more effective to have a higher voltage than lower voltage. Ex: a 48v system vs 12v system. The 48v system will require 4 more batteries for the same amp hour rating, but that amp hour rating is at a higher voltage so for a given load it will require less amps to get the same wattage.

Normally to get a rough idea I just do amps times volts myself. So a 100ah 12v battery would be 1200wh. Though keep in mind you really want to not go past 50% so if you are sizing a solar system or what not you want to double whatever it is you figure you need.

 

[JEDI]

Normally to get a rough idea I just do amps times volts myself. So a 100ah 12v battery would be 1200wh.
Though keep in mind you really want to not go past 50% so if you are sizing a solar system or what not you want to double whatever it is you figure you need.

that's for lead-acid batteries (same as car batteries).

thought drain to 0% it doesn't matter for nimh or li-ion rechargeables?

 

[Red Squirrel]

Li-on can discharge a bit more, but even then I would not bring them down to 0%. Basically you monitor the voltage, and try to not go below a certain voltage. For lithium ion I think around 3v is the minimum you want to let it go down to.

Really depends on application though. For something that will be discharged all the time, you want to be more conservative but for something like a UPS you can probably push them a little further since they won't be used every day.