Deep cycle voltage drop ?

I didn't realise deep cycle batteries were specified by their CCA?

Anyway: in general it's not a good idea to allow any battery to fall below 10.5 volts minimum it will shorten their life - 11V is better and, to be honest, the amount of power you can draw between 11V and 10V5 is not a lot anyway.

Mike Harding

Hi there bucky, I'm with you there I thought that was the idea of a deep cycle battery was that you can completely drain it and then recharge without killing the battery. I thought that was the idea of a deep cycle other wise you might as well just get an ordinary battery at half the price, Ive always believed this, oh well lets see who is right. Regards Steve M

What is the battery model - without that we are only guessing.

AGM batteries are rated for both CCA and can still be deep cycle.

The cutoff voltage for a particular level discharge depends totally on how much current you are drawing at the time.

Mike

Very interesting topic. Any winch competition people out there care to answer this one? I regularly hear winch people say that they were down to about 8 volts ! Don't hear them complaining about having stuffed batteries though.

People readily quote “your battery is 50% discharged when it reads 12.xx volts” - but these no-load voltages are useless unless you want to wait hours after you stop charging or discharging the battery to take the voltage reading.

If you are measuring the battery voltage (directly at the battery terminals, not somewhere along the wiring) you need to use a totally different table of voltages. Unfortunately this varies with battery type, size and temperature, so there is no single “correct” table.

e.g. if you want to leave 50% capacity in an N70 size battery then you should stop discharging at 9.4 volts - IF you are discharging at 340 amps. Or stop at 12.4 volts if you are discharging at 5 amps.

Of course these voltages will change with battery type, battery age and temperature.

I've been collecting some info on Voltage+Discharge current versus capacity and not surpisingly it shows inconsistencies between different sources of information. At least these figures will let get closer than the "no current, battery rested for 24hrs" figures that every quotes, but are very inaccurate when the battery os actually powering fridge etc

---------0x-----0y-----0z-----0w----3----4.5---22---90--270---340 - Discharge Amps
100% 12.70 12.66 12.80 12.80 12.5 12.8 12.5 12.2 11.6 10.4
80%- 12.42 12.49 12.64 12.55 10.2
60%- 12.20 12.32 12.48 12.30- 9.9
50%- 12.06 12.24 12.40 12.18 12.4 12.2 12.0 11.8 11.3 9.4
40%- 11.90 12.16 12.32 12.06- 9.5
20%- 11.58 12.06 11.96 11.82- 8.9
--0%- 10.50 11.89 11.80 11.60 10.6 10.8 10.4- 9.5- 9.4- 6.0

Sources for these voltages

0x - unspecified battery www.windsun.com/Batteries/Battery_FAQ.htm#AGM,%20or%20Absorbed%20Glass%20Mat%20Batteries

0y - Low Maintenance (Calcium Lead) Battery - www.uuhome.de/william.darden/carfaq4.htm
unspecified battery www.batteryuniversity.com/partone-13.htm and Site Link

0z - Maintenance Free (Calcium-Calcium) or VRLA (AGM) - www.uuhome.de/william.darden/carfaq4.htm

0w - Odyssey Staring Battery Handbook.

4.5A-270Amp Absorbed Power N70-size 90AHr AGM deep cycle battery - http://www.absorbedpower.com/battery/pdf/AP-GT12-90C-01Sep05.pdf

3A, 340A 60 AHr unspecified battery - Site Link

Mike