How Deep dare I cycle the Deep Cycle battery?

Depends how long you want it to last.
50% is the recommended maximum discharge for regular use.
An occasional 55-60% is probably OK for emergencies, but don't plan on doing that regularly.

Cheers,
Peter
OKA196 Motorhome

Welcome to the real world ,.... when is 105ah battery not a 105ah battery...when you can only discharge it down to about 50ah before you have to recharge it....so in reality you only have a 55ah battery....feel dudded ?....and it is recommended that you only recharge the said battery at a rate of no more than 10% of its capacity and in yours and mines case that is 10 amps or thereabouts....cheers and happy discharging and charging

Why do waeco have those settings?

I agree with Bruce, he is spot on. You actually "ruin" a battery a little bit every time you discharge it. The deeper you discharge it, the more you ruin it. This why batteries do not last forever. You should never let a battery or battery bank go below its nominal voltage EG 12v. The rest is up to you, at the end of the day, its all about how long do you want your battery to last.

Thanks for all these posts they're very informative!

I just called to buy another deep cycle, a marine shop is offering a 125ah for the same price as my Hella 105. How does one choose a d c battery? Any questions or checks before purchase?

The supplier is always going to play safe & recommend a charging regeme that will be easy on the battery. My experience with quality deep cycle's is you can discharge to 11.8 volts as many as 50 times & still get over 4 years life. While not ideal for maximum life in reality most cars simply dont have the space to carry 200ah's + & people are usually happyg to live with a 3 or 4 year life span anyway.
Cheers Craig..............

The 12.2V most give as an indication of state of charge of a battery at 50% is an open terminal voltage. Any load on the battery will lower this reading.
Try measuring the open terminal voltage, it will be higher.

I just read across my battery running a Waeco 110 litre and it shows 11.96volts.
If I disconnect everything using this battery the open terminal voltage is still 12.41V.

I think the 11.8V cut-off on the Waeco is fine for about a half discharged battery.

You will find that it doesnt make a lot of difference how deep you discharge it. Each battery has a certain amount of amphours that it is good for. If you discharge to 50% then you will get maybe 700 cycles out of it. (700 x 50 = 35000 Ahrs).
If you discharge to 20% you will only get maybe 400 cycles out of your battery. ( 450 x 80 = 32000Ahrs)
These figs are from the factory specs of my AGM battery.
So just accept that the battery has a limited life and live with it.

Ian

Dont forget to take temp into account as well. Most batt manufacturers cycle test at 25deg C. Exide state that for deep cycle wet cell, battery life is halved for every 10deg C above 25deg C. So keep your batteries cool as you can especially while charging and discharging. If you use your batteries once or twice a year on the big trip, it is not going to matter that much. If your use is more like weekly then it pays to look after them. Dave

Firstly to all those who advocate that "batteries will die anyway so why bother looking after them", I wish I was selling batteries to you.
As an electronic engineer with over thirty years experience designing, installing and running telecommunications equipment on 50V banks of batteries on what might be called an industrial scale, I find this topic interesting. Sorry to disturb your new year if you don't.

I'm trying to answer a members reasonable question without getting too scientific.
The initial question was simply why does Waeco have their battery monitor cut off set at what seems to be a very low threshold. The newer waeco models have three "modes" that can be set. These are Low, Medium and High. The cut off voltages are 10.1V, 11.4V and 11.8V respectively.

To most people these seem very much below the suggested lower value for a 50% discharged battery of 12.2V.
I simply made the point that the 50% discharge voltage of 12.2V is an open circuit voltage and should not be confused with the voltage seen by the fridge when its compressor is running.

I did the tests again last night. Set the monitor "mode" to medium expecting a cut off at 11.4V.
The fridge behaved as expected and cut off when 11.4V was reached during compressor operation.
The battery was then tested in open circuit configuration and found to read 12.26V.
A specific gravity reading was then taken and found to read 1205. These readings are indeed consistent with the battery being at just under 50% discharge.

If a person wants to keep their batteries as much as possible above the 50% discharge level then the waeco monitor works for this even if at first glance the figures could be somewhat misleading.

I don't know why it all has to get so complicated by some.

Waeco Shopper,
I'll think you will find that the settings have more to do with you being able to start the car in the morning (yes I know you are using an Aux battery however Waeco doesn't know that) and not a lot to do with your Aux battery condition.
It would be perfectly acceptable to have the starter battery ACCASIONALLY go as low as 11.8 overnight and still be able to start the engine in the morn.
But most of us prefer to run our fridges via Aux batteries just in case.

The point is not how far can you can discharge it to but more about how long can I keep the SOC up as high as possible.
I also assume you have the battery charger connected to this battery now ( given your on the net) and not just running on the battery alone???
Cheers
Trevor

If you don't have an accurate method of measuring state-of-discharge, is there much point in wondering about cut-off point ?

I use a Watts-Up power meter to tell me state-of-charge - it continually measures current flow and accumulates this, so that I know how many amphours have been drawn from the battery.