100Ah 12v Battery voltage under load

[Ian]

Bit of a random question... but maybe someone here will know!

I've got a 100Ah deep cycle gel leisure battery which is hooked up to a 3000W inverter (not using it near full capacity). I'm measuring the current voltage across a shunt and displaying the results on a meter, which should give me a better idea of the in-use battery condition, rather than a simple voltmeter that would only give an accurate reading when there is no load.

When I'm using a large load (i.e. 1000W, about the max I'd use), the voltage drops to about 11.6v in use. My cabling is 35mm so I don't think that's the issue here as it can handle high current just fine. Can anyone advise on what is the lowest voltage drop I could allow without damaging this sort of battery? I know that I can't let this voltage drop to below ~12.2v when there's no load, but it's the high load voltage I'm interested in.

I've had a good search and read up, but I get a lot of different results. Most focus on the 12.1-12.2v max discharge voltage, rather than the drop during load. Those that mention it don't give much of a guide. Hoping someone here has experience!

 

[V_R]

You lost me at 'deep cycle'

Sorry!

 

[muckshifter]

In the Marine World a drop to 11.6 could be interpreted as a damaged battery.

How To Maintain Batteries - Deep Cycle Battery Store

THE BASICS ON BATTERIES *Important Items Highlighted/Colored First things first. A 12-volt battery is not a 12-volt battery. Twelve volts is just a nominal, convenient term used to distinguish one battery from another. A fully-charged 12-volt battery, allowed to “rest” for a few hours (or days) with

deepcyclebatterystore.com

 

[Ian]

Cheers @muckshifter, that's one of the pages I was reading. From what I now understand, as long as the battery doesn't drift too far away from 12V whilst under heavy load, I should be OK - as it's not going to damage the battery chemistry. If it's at resting voltage, I should try and keep it about 12.2v on my particular battery.

 

[crazylegs]

Cheers @muckshifter, that's one of the pages I was reading. From what I now understand, as long as the battery doesn't drift too far away from 12V whilst under heavy load, I should be OK - as it's not going to damage the battery chemistry. If it's at resting voltage, I should try and keep it about 12.2v on my particular battery.

So does that mean your battery is shot Ian, how old is the Battery?
Is this a campervan setup?

 

[Ian]

The battery is brand new and OK, I'm just not sure how hard I should be pushing it. I heard back from the retailer today and they sent me a handy discharge graph which shows how hard I can expect to push it. I've been really impressed with their tech support. Here's the graph in case it's any use to anyone in future (attached).

They suggested I limit to 25A discharge if I want the battery to last a long time, which is OK by me - it won't often be used with the inverter for heavy loads. I'm mainly using it as a battery backup in my workshop and because I sometimes need to use powertools for jobs on the road and don't have power nearby. I'll likely also use it to power my telescope from a 12v socket .

 

[crazylegs]

Ahhh gotcha

I take it you know not to discharge below 50% charge in AGM cells for the longevity of the battery, looks like your just going to be within parameters.

 

[Ian]

Cheers @crazylegs, yeah I want to try and keep the battery in good condition for a long time, so will avoid discharging it past 50% .