Comparing NiMH and LiFe battery capacities for transmitters

[Monkeysmate]

I'm struggling to get my head around the different battery capacities.
My lad's MT-S transmitter takes four AA batteries, and we're using NiMH rechargables with 2900mAh capacity.
I'm contemplaiting getting a LiFe battery for it though, as they seem to last much longer in my other son's MT-4S.

What I don't get is why a 6.6v 1000mAh LiFe battery lasts so much longer than 4.8v 2900mAh NiMH.

Can any of you electrical boffins explain?

Is it just that the NiMH self-discharges at a much higher rate than LiFe?

Ta

[mattr]

It's related to the power delivered. Which is a combination of volts x amps. More volts requires less amps to produce the same power.
And the shape of the discharge curve has an effect
The nominal voltages stated are based on the discharge characteristics.

Used to take my LiFe battery about 6 hours use to actually get down to 6.6 volts (fully charged is 7.2 iirc). The Nimhs used to hit 4.8 in about 20-30 minutes (fully charged is 1.25 per cell or so).

Not a boffin. Just work with hybrid cars and electronics/software all day

[Monkeysmate]

Ace. Thanks

[dodgydiy]

also metal hydride has a greater self discharge rate, typically losing up to 50% charge per week with standard cells, whereas lithium cells lose virtually nothing. hybrid nimh cells are available, often called precharged nimh, they have a much lower self discharge rate as they are designed to give a lower current output, perfect for electronic devices like cameras or transmitters, using Gp recyko pro in mine, charge once every couple of months

[ianjoyner]

Originally Posted by Monkeysmate

Is it just that the NiMH self-discharges at a much higher rate than LiFe?

Yes I think this is the main factor.