# 12 volts deep cycle battery

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#### mrel

Jul 2, 2008
115
Hello

Have a 12 volts battery deep cycle AGm 100 Ampere hour.

Question is : If have load draw 1.34 amp hour ,would the 12 volts battery maintain the 12 volts for 50 hour?

Somewhere read someone saying if have 100 amp hour battery mean that a load that only draw 1 amp an hour can provide 1 amp for 100 hours, is that right?

mrel

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,809
would the 12 volts battery maintain the 12 volts for 50 hour?
No. The voltage will decrease with time. first slowly, then increasingly fast. See e.g. this lead acid discharge curve.
But, to start with, a fully charged 12 V lead acid battery doesn't start at 12 V, more at 13 V or a tad above.
If you need reliable and exact 12 V, you'll have to add a SEPIC regulator which can regulate downwards (from Vin > 12 V) and upwards (for Vin < 12 V).

omewhere read someone saying if have 100 amp hour battery mean that a load that only draw 1 amp an hour can provide 1 amp for 100 hours, is that right?
Nominally yes, 100h * 1 A = 100 Ah. However, even a deep cycle battery should not be discharged to 0% plus the capacity (100 Ah) is given for a defined load (see your battery's datasheet) and may be more or less depending on the actual discharge current.

#### majoco

Nov 10, 2019
50
Wiki says:
A deep-cycle battery is a battery designed to be regularly deeply discharged using most of its capacity. The term is traditionally mainly used for lead–acid batteries in the same form factor as automotive batteries; and contrasted with starter or 'cranking' automotive batteries designed to deliver only a small part of their capacity in a short, high-current burst for cranking the engine.

For lead-acid deep-cycle batteries there is an inverse correlation between the depth of discharge (DOD) of the battery and the number of charge and discharge cycles it can perform;[1] with an average "depth of discharge" of around 50% suggested as the best for storage vs cost.[2]

The Ampere-hour capacity of any battery is entirely dependent on the rate you discharge it. Most vehicle batteries are measured at the 10 Amp rate down to 1 volt per cell. We used to test aircraft NiCad batteries at the 40 Amp rate and metered every cell - if it didn't meet the specs then we would change the cells that went down first - then there was a long procedure that discharged every cell down to zero, let it cool then charge to full capacity plus 40% on a two-step charge and then retest - hopefully it passes! The dud cells we pulled out worked very well when made into 12volt car batteries!

So theory your 100Ah battery should last about 75 hours (as you are only discharging it at 1.34Amps) before it gets to the end point, say 1 volt per cell. At this point you should take it out of service and immediately recharge it.

#### Bluejets

Oct 5, 2014
7,097
1V per cell...I think you need to do some serious reading there.
Best place most have found for any battery details is the Battery University site.

#### Ylli

Jun 19, 2018
411
When I worked on Gel Cells, they were always rated at the 20 hr rate. A 5 Ahr battery could deliver 0.25 amps for 20 hours. Any discharge rate higher than the 20 hr rate would lead to a reduced capacity.

#### dave9

Mar 5, 2017
1,190
It might help if you described the project you intend for this battery. If the load is resistive then it will draw more current at higher, fully charged battery voltage and less as the battery voltage drops while it discharges. If the load has a regulated power circuit in or between it and the battery, it, may do the opposite and draw less current from higher voltage and more as the voltage drops.

Since the voltage variance for good lifespan of lead acid is not terribly large it may not make that much difference, since you are not supposed to fully drain the battery so you get good lifespan out of it.

The best test is use the battery to power the load. If you don't have the battery yet and feel its capacity is borderline, move up to a larger battery or two in parallel, but then they should be a matching chemistry and charged in parallel too, so they have no deviation in voltage.

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