Thread: Battery Reserve Capacity, please explain.

Hi HangOver, basically Reserve Capacity ( RC ) is used to give a true indication of the amount of storage capacity a battery has.

It is based on the amount of time it will take a fully charged battery to be discharged to 10.5 volts using a constant 25 amp load.

This is a much better way to determine how useful a given battery will be when used as an auxiliary power supply and is a far more relevant rating than a CCA rating when trying to decide which is the better battery to used as a deep cycle battery.

A battery can have a high CCA rating but have a very low RC rating, making it good for starting the vehicle but likely to have both a short operating time from full charged to discharge and worst still, is likely to have a very short life span when used a a deep cycle battery.

Stating batteries are usually not RC rated as they are not intended to supply power for more than a few seconds at a time.

in addition, the current draw (25a) and drop off voltage (10.5V) at the determined time is whats considered the "duty cycle" of the battery which means if you know your expected draw off of the battery and its expected charging you can also work out roughly the life expectancy of the battery and vice versa by monitoring the voltage on the battery and how long it takes to hit 10.5v from a full charge compared to it RC rating will tell you roughly how healthy the battery isnt.

so why 10.5 volts?

Is that the voltage considered dead flat; too flat to crank.

Or is that considered the voltage the battery should not drop below to avoid any damage to the battery?

actually while I have the attention of two people who know what they are talking about

I just bought a 350w amp, (cheapest I could find)

the specs are:

350 Watts max power (4Ω bridged)
Rated power output 2 x 55W into 4Ω load, 2 x 75W into 2Ω load
Is this correct:
Its running two 4 ohms speakers so power draw will be close to the output so it will draw about 110w or 9amps?

If that is correct why is it filled with a 20amp fuse?
Am I just confusing music power with actual current draw, is it different?

Hi again HangOver, your battery is usually too flat to crank at a voltage of 11.25 volts but the battery will still have some stored capacity in it to run a fridge or some lights.

10.5 is a flat battery with no capacity left.

Originally Posted by HangOver

350 Watts max power (4? bridged)

As to your sound system, have a look at the specs and see if they have an actual maximum amperage listed.

350 Watts usually refers to the available power for the speakers and not the power consumption for the amp.

350 watts would be about 30 amps amps at 12 volts and would be one huge current draw.

Cheers

the manual says :


Operating voltage 14.4v (11v-16v allowable)
Current consumption 17amps

So i guess a 20amp fuse is correct as a 15amp would (I assume) keep blowing.