Electrical Battery & Dual Battery Question

[CraigE]

Leading on from a previous post by another poster, my cranking battery appears to have died, will charge but not hold. Now I elected to replace it with a SSB 1000CCA 130 AH battery same as secondary battery. They just fit. What I did notice in the Defender is it has 2 large diameter earthing cables. Now originally they both went to the negative of the cranking battery. When the dual battery system was fitted one was fixed to each earth.
The set up like this kept showing a charge rate of 13v going to secondary battery, but all else worked fine.
When I changed the batteries I hooked them both back up to the cranking battery just to test.
Well the second battery now shows a charge rate of 14v same as cranking when being driven, but for some reason initially high beam would not work (low beam fine) and when they did start working seem to be really dull.
Got me stumped.

[trout1105]

Have you tried replacing the earths to their original position and running a fresh new cable to the auxiliary battery?

[CraigE]

Have you tried replacing the earths to their original position and running a fresh new cable to the auxiliary battery?
The cables are good. Might change it back tomorrow and put one of the large earths back to the aux battery.

[trout1105]

I am thinking that one of those dual earths that connect to the cranking battery is used for the headlights and fitting a separate new cable for the aux would fix your problem.

[bee utey]

Dual earth cables would suggest one to the engine/trans and one to the chassis/body. They should not be separated.

[CraigE]

Dual earth cables would suggest one to the engine/trans and one to the chassis/body. They should not be separated. Might try earth to earth

[sierrafery]

IMO the dead battery had some internal short which caused a voltage drop on the whole setup and now with the good one everything is back to normal, also when different power batteries are used in a dual system this can happen due to the different internal resistance of the batteries so having similar batteries is the best choice... if it will still make tricks better replace the alternator's regulator cos it's quite common for them to fail and cause voltage drop under load ... see description: Land Rover Discovery & Defender TD5 Series 2 Alternator Regulator 98-06 - Starter Motor Repair Kits Starter Motor Repair Kits (http://www.startermotorkits.com/listing/land-rover-discovery-td5-series-2-alternator-regulator-2/)

[350RRC]

IMO the dead battery had some internal short which caused a voltage drop on the whole setup and now with the good one everything is back to normal, also when different power batteries are used in a dual system this can happen due to the different internal resistance of the batteries so having similar batteries is the best choice... if it will still make tricks better replace the alternator's regulator cos it's quite common for them to fail and cause voltage drop under load ... see description: Land Rover Discovery & Defender TD5 Series 2 Alternator Regulator 98-06 - Starter Motor Repair Kits Starter Motor Repair Kits (http://www.startermotorkits.com/listing/land-rover-discovery-td5-series-2-alternator-regulator-2/)

Yep, Redarc used to recommend same batteries with their isolator which I have.

I had a brand new Exide aux battery go to an early grave alongside a Willow.

Now both Willow for 2 years and showing perfect voltage for my POS, hopefully for the next 10 years like the the last Willow.

DL

[drivesafe]

Hi DL, when using a DC/DC device or a battery charger, unless it is set up correctly, you can have problems when trying to charge disimilar batteries.

This problem does not exist when charging mixed battery types with an alternator.

NOTE, if you set up a DC/DC device or battery charger correctly, you can safely charge mixed battery types.

[350RRC]

Thanks Drivesafe,

I have nowhere near your expertise in these matters, just relaying my experience with batteries and isolators.

Do you have a view on why Redarc would have suggested using similar batteries in dual set ups?

Also...... the Exide was only earthed to the body, whereas the much older Willow was obviously earthed to the body, chassis, etc as the main cranking battery.

Would this have caused an issue? Have noted the earlier post about common earths.

cheers, DL

[drivesafe]

Hi again DL, just about all DC/DC manufacturers state to only use similar battery types with their DC/DC device.

The reason for this is that to get an advantage from their device, you set the device to charge a specific type of battery and this then allows the device to TOP OFF that type of battery using the maximum safe voltage that that specific battery type can be charged at. Allowing the battery to be TOPPED OFF quicker that what some alternators can do.

This is one of the few advantages a DC/DC device can offer over charging with an alternator, but the draw back is that all the batteries must be of the same type, or you can damage one or more of the batteries by over charging them.

As posted earlier, this is not a situation that occurs when charging with an alternator.