Understanding battery ratings

[DavidPV]

I want to learn how the battery ratings work. e.g.

1-100Ah @ C100 rate.

and

2. -100Ah @ 12 hrs
   
3. - Apart from these two critical terms, CCA (Cold Cranking amperes) is another terminology, and from my understanding, it is the rating of how much surge can a battery accept fro starting loads, in particular for induction loads (motor type- pump, Air condition etc...).
   
   

Any input would be appreciated.

Dave.

[Baling Wire]

Dave

Check this site out.

http://www.batterystuff.com/tutorial_battery.html

BW

[Flux]

Batteries are rated in Ah. In the perfect world it wouldn't matter if it gave 1A for 100 hrs or 100 A for 1 hr or 50A for 2 hrs.

A real battery shows a higher capacity when discharged slowly then with a heavy discharge so you need to quote the capacity at a known point ( often C20). The difference in the ratings can be sorted out if you take into account an equation devised by Peukert but it is complicated.

case 1 at C100 rate it would take 100 hrs to discharge and the current would be 1A.

Case 2 would be discharged in 12 hrs so for 100Ah the current would be 100/12 = 8.4A

Batteries intended for RE don't have a cranking duty, that is for starter batteries for vehicles where the thing needs to produce large currents for a starter motor. It is something like the amps it will provide for a certain time until volts drop to a given figure, I don't claim to know the details, it is rarely used in the UK.

Deep cycle batteries for our sort of duty are built with thick plates and can not manage these high currents but they have a far longer life. No it has nothing to do with inverter surges.

If anyone tries to sell you a battery with a cranking amp rating then it is a car battery not a true deep discharge beast. Some claim to be a hybrid with cranking ability but thicker plates for longer life. They make poor starter batteries and are useless for serious deep discharge, they are often called marine batteries ( perhaps boat engines are easier to start).

Flux

[bob g]

if you see a cold cranking amps rating,, you are looking at the wrong type of battery for RE use.

i know they are sold as deep cycle batteries, but their ability to do so is only marginally better than a car battery, and woefully short of what a true deep cycle can deliver.

i know of no true deep cycle that has a cca rating associated with it.

100, 20 and 8 hour ratings are basically how many amp the battery can deliver

over time.

a 100amp hour battery can deliver 1 amp for 100 hours, 5 amps for 20 hours, about 12 amps for 8 hours,, (more or less), until it is dead. which is not what you want to do anyway,,

myself i would figure on no more than a 50% depth of discharge, before recharging, so each of the previous numbers get cut in half (roughly)

others will explain this better than i have,, surely.

bob g

[Ungrounded Lightning Rod]

Marine batteries are designed and rated as a middle-ground between a deep-cycle and a cranking battery because (especially in a small boat with only one battery) they are generally called on to do both:

They crank the engine - occasionally.  Maybe twice on an outing (once to go out, once to come back).  And they engine(s) they start are normally at a moderate temperature (or at least significantly above freezing) and usually well maintained.  So they usually start quickly.

They serve as a "house battery" to power navigation marker lightning, instruments, radios, cabin lighting, bilge pumps, and so on.  They do this for hours or even a day or more at a time with the engine off.

This is true of both power boats (which may spend hours powered down while the occupants are fishing or anchored out overnight while occupied) and sailboats with auxiliary engines (which usually run only at the start of an outing to get away from the dock, at the end to get back in, and maybe for a half-hour or so if the boat is becalmed).

As with a travel trailer or big RV, a larger boat may have separate house and cranking batteries.  In that case each can be a type optimized for its particular service.  (Even then the house battery may be called on to crank in a pinch, or the cranking battery to do non-cranking work if the house battery is exhausted.)