Thread: D4 - Lithium AUX battery under the bonnet.

I did further contact DCS last year and asked some questions. End result is I'm keeping standard setup. ie AGM starter and Traxide. Here is the email reply I got from DCS Sales Engineer.

"Hi Trevor,

Thanks for reaching out, the Disco 3’s run a normal voltage regulated alternator it’s quite stable. The issue with the Disco 4 alternators is they run output voltages above 15.0V, warranty on the batters is only valid up to a absolute maximum alternator voltage output of 14.60V so it’s not a good idea. Focus one getting an auxiliary battery inside the cabin and keeping a wet cell for engine starting, plenty of bundle options here: Battery Bundles


Regards,

Paul Tomolowicz

Sales Engineer & Product Development"

Hi Briar and thanks for posting up DCSs info, and they sound like they have no real clew as to what vehicles can actually have Lithium cranking batteries in them.

D3s have the basics of a SMART alternator system and while they never go below about 13.4v, which is ideal for charging lithium batteries without discharging them while you drive.

But my D3 saw voltages as high as 15.1v and I have customers overseas how have reported voltage readings as high as 15.5v, in cold climate countries.

Their info on D4s is not correct, where any D4, programmed for running an AGM cranking battery, will have a maximum voltage of just 14.8v but the high end voltage is not the problem.

Because D4s operate a true SMART alternator, D4 alternators can run as low as 12.2v and this is an absolute No-No for lithium batteries, for a number of reasons.

As I posted earlier in this thread, when ever a SMART alternator runs at less than 13.2v, the vehicle will draw its power from the lithium battery and on long trips, will actually flatten the lithium battery.

But if you drive long enough to cause the lithium battery to go below 12.5v, a near flat Lithium battery, the D4s BMS will see a low battery and run the alternator at 14.7v.

With the huge alternators in these vehicles, you could be getting as much as 180 to 200 amp going back into the flat lithium battery.

This is another No-No for most lithium batteries, especially as it could be charging at these ultra high current for some time.


The only way to have a lithium battery in any vehicle with a SMART alternator, is by charging the AUXILIARY battery with a DC/DC device and forget about using a lithium battery as a cranking battery.