Lithium battery dilemma

Albynsw

Well-Known Member
I am setting up my power requirements to run two fridges and currently have a 100a/h Itechworld lithium. Normally that would be plenty of capacity for our usual style of touring as I used to do the same with a 110ah AGM but we would move most days with occasional stay of max 3 nights
My concern is that I will be underdone on this next trip as I plan to move a bit slower. I have a permanently mounted 200 watt solar plus an additional solar blanket to help it all along and we will be traveling the northern part of Australia so should see plenty of sun.

Now I thought I would add another battery to give me more backup but the problem is my battery is out of stock for the next 5 months and they tell me I cannot parallel another battery with my current one, they need to be identical
What do you do, start again with new compatible batteries or install a battery switch so you can manually switch between battery types or…….?
 

Rusty Panels

Well-Known Member
I don't know much about the subject but have heard pretty much the same story regard mixing and matching. I'd reckon that you might be best off to use a manual switch as a temporary solution till you can pick up another lithium to match. Are you looking at buying directly from iTechworld as there's no mention of low stock on the site?
 

Albynsw

Well-Known Member
I don't know much about the subject but have heard pretty much the same story regard mixing and matching. I'd reckon that you might be best off to use a manual switch as a temporary solution till you can pick up another lithium to match. Are you looking at buying directly from iTechworld as there's no mention of low stock on the site?

It is the slimline version which they have marked as sold out. I have rung them to confirm and that I can’t use any of there other batteries with mine
 

Rusty Panels

Well-Known Member
I like the idea of generator back up and have a little Honda 2200 inverter. I was going to take it with us for the caravan but finding room is the biggest issue. There is a compartment in the front of the van but I have it chock a block with other gear. The 300w of solar seemed to do the job along with juice from the alternator when on the move. Everyone reckons we'll never need it but Murphy's law tells me different.
 

CTL

Well-Known Member
How old is your fixed solar and also your blanket?
How are these connected to the battery?
 

Albynsw

Well-Known Member
With that much solar I would think you won’t have a problem given you will be in n the northern parts of Australia , I would just get a small generator as an emergency back up which is what I am doing for our 3 month trip later this year

Not willing to sacrifice room or weight for a genie, would run the car at idle if necessary to top up batteries, I think I get close to 20 amps at idle with dc dc charger
 

Mick_Marsh

Active Member
Now I thought I would add another battery to give me more backup but the problem is my battery is out of stock for the next 5 months and they tell me I cannot parallel another battery with my current one, they need to be identical
Yes, if they are connected in series, they need to be matched.
But not in parallel.

If they "need to be identical", why?

  • Connecting batteries in series increases voltage, but does not increase overall amp-hour capacity.
  • All batteries in a series bank must have the same amp-hour rating.
  • Connecting batteries in parallel increases total current capacity by decreasing total resistance, and it also increases overall amp-hour capacity.
  • All batteries in a parallel bank must have the same voltage rating.
 
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CTL

Well-Known Member
Both are brand new and will be connected through my Enerdrive dc2dc charger
Ok, so panels will be at max efficiency for the first year, excellent. But consider if you want to park in the sun when necessary?
The Enerdrive is programable. Mine will add 40 amps at idle with my 90 amp alternator. I have not found the need to carry a gennie
 

Lost1?

Well-Known Member
Not sure if this helps. I can run a Dometic 75L dual zone fridge for up to 3 days if one side is at -5 and the other is set at 4 degrees off a single 100ah lifepo4 battery. This is in summer time.
Not sure how big your fridge and freezer will be though.
 

Albynsw

Well-Known Member
Not sure if this helps. I can run a Dometic 75L dual zone fridge for up to 3 days if one side is at -5 and the other is set at 4 degrees off a single 100ah lifepo4 battery. This is in summer time.
Not sure how big your fridge and freezer will be though.

Thanks for that, is that assisted with solar? I am running a 40 litre everkool fridge drawer and a 75 litre upright fridge, both will be run as fridges only.
 

Albynsw

Well-Known Member
I thought I may of found another identical battery today from a reseller but no go. I am thinking I will just buy a separate battery in a battery box and carry with me and manually swap them over if needed
What do others think about this, should I just run with my current battery and rely on solar or running the car in situations where I need it?

I am happy not to be carrying unnecessary bulk and weight but at the same time don’t want to be constantly concerned about the state of battery charge
 

Lost1?

Well-Known Member
If you are running a laptop or charging camera etc then 200AH of battery is probably needed. Running my fridge at4 and 2 degrees I can go for 4 days without any charge. So if you are only running fridges you should be ok with the solar and battery you currently have.

Remember the drive will top the battery up and if your solar is hard wired it will take over as soon as the engine turns off.
 

Albynsw

Well-Known Member
We are not heavy power users, no laptops, coffee machines, pie warmers etc just 2 fridges and some lights

Thanks for the feedback
 

boobook

Well-Known Member
Yes, if they are connected in series, they need to be matched.
But not in parallel.

If they "need to be identical", why?

  • Connecting batteries in series increases voltage, but does not increase overall amp-hour capacity.
  • All batteries in a series bank must have the same amp-hour rating.
  • Connecting batteries in parallel increases total current capacity by decreasing total resistance, and it also increases overall amp-hour capacity.
  • All batteries in a parallel bank must have the same voltage rating.


That website applies to lead acid or standard cell batteries and is not applicable advice for Lithiums.
.
The reason you need to heed the manufacturers advice is that 12v lithium batteries are really 4 x 3.7v batteries, plus a BMS. The power goes through one or more MOSFET transistors in the BMS. There are thousands of these with different ratings for the manufacturers to chose from. So mixing and matching lithium batteries in series or parallel will almost certainly mean one battery is favoured over the other which may get destroyed or not even used.

You will see almost all lithium manufacturers specifying a limit to the number of batteries in series or parallel and all will stipulate that the batteries must be the same AH and type.

For Alby, a way to add a second, different Lithium battery is to charge it separately with the DCDC. Or direct from the 12v line. Then if you need to dip in to the extra 100 Ah, you can connect it as the input to your DCDC manually. You'd want to have a later purpose for that second lithium though.

I do this to use my car's aux AGM as a booster for my lithium in the camper. I trigger it with a small switch on one of the mode input wires on the redarc DC DC. If you have some interest I can give you more details.
 
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Triton14

Well-Known Member
If you used to run the same system/items with a 110Ah AGM then you already have more usable power with a 100Ah lithium.

The way I understand lithium's is that you can safely use 90% of the charge so 90Ah for a 100Ah battery, where as with the agm you could only use 50% 55Ah.

So you are 40Ah better.

Im not up on lithium's & I know there are better ways to work that usage out but to me you are still way ahead in usable power with the lithium.

With the solar you could probably go 5-7 days without have to even having to start the car?
 

RBJET

Well-Known Member
My fridge runs indefinitely off 12AH AGW and 120W of solar so I highly doubt you'd have any issues with that amount of solar and battery power.
 
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