Thread: Who has fitted a battery behind the second row of seats in a D3

I fitted an 80ah AGM on its side in the centre of the 3rd row footwell of a D4. A 50A cable was fed through the firewall behind the battery then along the sill tread-plates before emerging under the 2nd row seats. The negative lead was bolted under one of the 2nd row seat mounting bolts.

Hi Sean, you will need a different DBS setup for that system.


Because a lithium battery has a higher settled voltage, around 13.2v, and because they hold this voltage level until they are around 80% discharged, they need to be separated from the cranking battery as soon as the ignition is turned off.


No conventional isolator will do this.


Because all lead acid batteries, be they AGMs or Wet Cells, they will have a WORKING settled voltage of no more than 12.75v.


So if you leave the two types of batteries connected, the lithium will continually back discharge into the lead acid battery.


This is great for the lead acid battery but will have a major effect on the longevity of the lithium battery.


You would actually be far better off just replacing the batteries you have and you will have more available battery capacity.


A 100Ah lithium battery has a usable capacity of around 80Ah and that is all you will have available, and this capacity is only going to be available if a lithium battery is recharged correctly.


If you stay with the battery types you are using now, first off, you will not need to loose the cab space.


Plus, your existing setup gives you between about 90Ah and 100Ah, depending on how low you discharge the Optima.


An Optima Yellowtop can be safely discharged down to 10.5v or 0% SoC.


But regardless of how low you discharge the Optima, you will still have more usable capacity.


Also, the Optima can be recharged quicker than the Lithium, and can be fully recharged at a lower voltage.


As usual, there is a lot more to this and I will post up more info if you require it, but you say your batteries are “on their way out”, why do you think they are on their way out?

Originally Posted by drivesafe

Hi Sean, you will need a different DBS setup for that system.


Because a lithium battery has a higher settled voltage, around 13.2v, and because they hold this voltage level until they are around 80% discharged, they need to be separated from the cranking battery as soon as the ignition is turned off.


No conventional isolator will do this.


Because all lead acid batteries, be they AGMs or Wet Cells, they will have a WORKING settled voltage of no more than 12.75v.


So if you leave the two types of batteries connected, the lithium will continually back discharge into the lead acid battery.


This is great for the lead acid battery but will have a major effect on the longevity of the lithium battery.


You would actually be far better off just replacing the batteries you have and you will have more available battery capacity.


A 100Ah lithium battery has a usable capacity of around 80Ah and that is all you will have available, and this capacity is only going to be available if a lithium battery is recharged correctly.


If you stay with the battery types you are using now, first off, you will not need to loose the cab space.


Plus, your existing setup gives you between about 90Ah and 100Ah, depending on how low you discharge the Optima.


An Optima Yellowtop can be safely discharged down to 10.5v or 0% SoC.


But regardless of how low you discharge the Optima, you will still have more usable capacity.


Also, the Optima can be recharged quicker than the Lithium, and can be fully recharged at a lower voltage.


As usual, there is a lot more to this and I will post up more info if you require it, but you say your batteries are “on their way out”, why do you think they are on their way out?

Thanks for the info. Why are things always more complicated than you think?
The cranking battery isn’t holding charge. Went camping to Moreton Island. Running a 65l fridge. The Traxide would isolate the cranking battery but wouldn’t turnover in the morning. I switched to the auxiliary battery as well. This struggled as well and a couple of mornings I had to use my lithium jump starter to get the D3 started.

I have a Traxide system in my D3 with an Ultima under the bonnet.
I also have a Thumper 75ah unit strapped down in the rear - I have totally removed the 3rd row seats and put in a false floor with tie downs.
I've got an Engel in the 2nd row, between the seats and it plugs into the Thumper, which is wired in to the Traxide system.
Everything works just fine, although there is only usually myself for going camping so I don't need a ton of storage space.
I'm happy to supply more info if needed.
Alan

Hi again Sean, how much use does your D3 get between trips?


Also, do you have a multi stage battery charger?


If so have a look at the link and see if this can bring your batteries back to life.


LONG TERM BATTERY MAINTENANCE


On-Line auto electrical info

Originally Posted by drivesafe

Hi again Sean, how much use does your D3 get between trips?


Also, do you have a multi stage battery charger?


If so have a look at the link and see if this can bring your batteries back to life.


LONG TERM BATTERY MAINTENANCE


On-Line auto electrical info

Usually long trips but can be a couple of weeks between. Have it connected to my Cetek MXS 10 charger when not using it. Will check out the link. The battery is about 3.5 years old. It’s a Century DIN85L MF.

Sean, based on the info you have supplied, if you follow the suggested charging cycles in that thread, my guess is that you will most likely recover the Optima, but I think there is probably a good chance you will partially or even close to fully recover your cranking battery as well.

If your batteries are stuffed, then you will just waste some time, but if they are recoverable, you could save yourself some money.

We fitted a 105AH battery(not lithium) on top of the drawers in the back while on our Kimberley trip, our Optima just couldn't cope with running two fridges in the heat up there, the new battery runs in series with our Optima under the bonnet which we had to replace at the same time, my fault really as I underestimated how old the Optima was before the trip.

All good now though.