Thread: lithium dual battery ideas

follow up question not worthy of it's own thread. I bought these terminal covers from some car shop can't remember which one
terminal cover 1.jpg

and they look like they're reacting with the plastic of the battery casing!
terminal cover 2.jpg terminal cover 3.jpg

they're not melting because I checked how hot they were getting after I noticed it. and also the cover on the positive was red but there is no red residue. and also the covers themselves after I peeled them away were whole and intact.

has anyone come across this before?! I assume they don't all have this issue?

That does look strange Maca. Never seen that happen myself.

How did your monitoring go?

I normally keep the USI-160 off (when the engine is not running) but decided to try ignition and shared mode for a few days.

Prior with the USI-160 off, the solar would keep the cranking battery topped up even on cloudy days.

With the USI-160 in ignition mode, and the two relays active, the solar was not able to get to the absorption stage - even on a sunny day.

With the USI-160 in shared mode, and with only one relay active, the solar today hit absorption stage on both batteries.

Not entirely a meaningful observation as the first few days of the test was cloudy, and the auxiliary battery was probably in need of a recharge so ran the engine for 30mins yesterday to give it a top up.

Once it stabilises again, will change back to ignition mode.

The aim of this test is to see how the solar charge controller reacts to different loads (and to make sure it can overcome the power draw from the USI-160 relays when solar output is low).

Originally Posted by Macadamia

follow up question not worthy of it's own thread. I bought these terminal covers from some car shop can't remember which one
terminal cover 1.jpg

and they look like they're reacting with the plastic of the battery casing!
terminal cover 2.jpg terminal cover 3.jpg

they're not melting because I checked how hot they were getting after I noticed it. and also the cover on the positive was red but there is no red residue. and also the covers themselves after I peeled them away were whole and intact.

has anyone come across this before?! I assume they don't all have this issue?

Any chance you can post a pic showing the terminal covers on the battery? (preferably with the wiring)

Originally Posted by drivesafe

Scroll down the page till you get to “Battery Maintenance”
https://www.aulro.com/afvb/the-verandah/246755-line-auto-electrical-info-8.html

for the past week I've had the aux battery out and performing this maintenance each night. Now every time I drive the car without fail the alternator is pumping out 14.7v for the entire drive. Where it used to do 14.7v initially then drop to ~13.3v then to ~12.3v it is now just a sustained 14.7v. is that because the cranking battery SOC is lower without the aux battery? is that how it works - in shared mode with the engine off, does the cranking battery "share" the aux battery capacity in the same way the auxiliary battery shares the cranking battery capacity - or is it one way only?

Hi Maca, my GUESS is that the two batteries were supporting each other.

Under normal driving conditions, your D4’s BMS can only monitor the cranking battery and it can NOT see what is happening with any other battery connected to the charging system.

This is done by the BMS monitoring the cranking battery’s negative terminal.

When you are driving with two low batteries, the charge is roughly halved. So for instance, you may have 100 amps available for charging, 50 amps will going into the cranking battery and 50 amps will begging into the auxiliary battery.

But the BMS only sees the 50 amps going into the cranking battery and the BMS may consider this to be an indication of an OK battery

With only one battery in the vehicle, the entire current load is now going into one battery and it is showing up at the BMS as the cranking battery is drawing too much load for a fully charged battery, and the BMS has decided to try to fully charge it.

A single 30 minute drive at 14.7v should have had your cranking battery near fully charged.

I would suggest you start by getting the cranking battery LOAD TESTED and then see what comes of that.

Also, at no time should your batteries be regularly discharged down 12.3v. For your D4 to discharge the battery down to 12.3v, the D4 will be applying about a 40 amp load to the battery while you are driving.

This kind of continuous current load is not good for any battery.

You also posted earlier that after each time you replaced your cranking battery you would see 12.2v. That would be very damaging to a new battery, to be discharged by a high current load, before the battery has been properly fully charged first.

As I have posted, your D4 appears to have a serious problem with the charging software, but I am not sure how you can fix this.


As I also posted, your D4 most likely has had a charging software problem from the day it came of the production line.

Originally Posted by drivesafe

When you are driving with two low batteries, the charge is roughly halved. So for instance, you may have 100 amps available for charging, 50 amps will going into the cranking battery and 50 amps will begging into the auxiliary battery.

But the BMS only sees the 50 amps going into the cranking battery and the BMS may consider this to be an indication of an OK battery

With only one battery in the vehicle, the entire current load is now going into one battery and it is showing up at the BMS as the cranking battery is drawing too much load for a fully charged battery, and the BMS has decided to try to fully charge it.

perhaps I'm not understanding you but sounds like you're saying with both batteries in, the BMS is undercharging them both and falsely assuming the cranking battery is fully charged but with just the cranking battery it's behaving normally and charging my cranking battery normally.

Also, at no time should your batteries be regularly discharged down 12.3v. For your D4 to discharge the battery down to 12.3v, the D4 will be applying about a 40 amp load to the battery while you are driving.

with a new cranking battery installed, both batteries in the car and in shared mode - on a long drive I would initially get 14.7v for a period of time, then 13.3v then 12.3v for a while before it jumped back up and down. does this not indicate the BMS considers the cranking battery is in a near full SOC and is reducing and turning off the alternator?
In any case why this hasn't happened since disconnecting the aux battery?

Found these BM6 battery monitors that log temperatures as well as voltage. As someone who loves data, I am interested to see how hot the batteries get in the engine bay and in general use. which may provide some information as to the suitability of lithiums in the engine bay. The app supports up to 4 devices [instead of having to pay for the third party 'multi battery monitor' app to monitor multiple BM2 devices].

BM61.jpg BM64.jpg

I was a bit worried they may use a bit more power than the old BM2 monitors but they seem pretty efficient.
standby power usage is around 1 milliamp [~0.8 to 1.1]
BM62.jpg

when connected to the app power usage is around 2 milliamps [~1.8-2.2]
BM63.jpg

This is interesting,in relation to Lithium under bonnet.



DCS Lithium LiFePo4 Update: Why I went back to Lead Acid (under bonnet) 2023 - YouTube