Fit another leisure battery

[Okta]

When I asked Google the question I got an AI overview, which must be right mmmm.

 

[trevskoda]

And should be connected thus.

 

[wildebus]

if you like AI info for advice, this might also apply:

When combining lead-acid batteries, it is important to match them as closely as possible in terms of capacity (Ah), voltage, age, and type to ensure optimal performance and longevity.

If lead-acid batteries are mismatched, several problems can occur:

1. Uneven Charging and Discharging
   
   • Batteries with different capacities will charge and discharge at different rates, causing some to overcharge while others remain undercharged.
   • Overcharging can lead to excessive heat, gassing, and water loss, while undercharging can lead to sulfation (the buildup of lead sulfate crystals), reducing battery life.
2. Imbalance in Voltage and Internal Resistance
   
   • Batteries with different voltages or internal resistance will cause an imbalance in the system, leading to one battery working harder than the others.
   • Higher-resistance batteries may not provide adequate power, while lower-resistance ones may take on too much load.
3. Reduced Performance and Lifespan
   
   • The weakest battery in the group will dictate the overall performance of the battery bank.
   • A degraded or lower-capacity battery can drain power from better batteries, shortening the lifespan of the entire system.
4. Potential Safety Issues
   
   • Overcharging and overheating can lead to thermal runaway, which may cause battery failure or even fire in extreme cases.
   • Uneven charge levels can cause electrolyte imbalance, which may lead to acid spills or excessive gassing.

Best Practices When Combining Lead-Acid Batteries:​

• Use batteries of the same type (Flooded, AGM, or Gel).
• Match batteries in capacity (Ah), voltage, and age.
• Ensure all batteries are in similar condition and state of charge before connecting.
• Use proper wiring techniques (e.g., balancing charge/discharge paths).

But AI is only as good as the information available to it

 

[Okta]

But AI is only as good as the information available to it

AI would carry more credibility if it attributed the information given to respected sources. I don’t necessarily disbelieve what it says and the knowledge might be sound but equally some of it might just be popular opinion which can be wrong. Hopefully as AI matures it will start to acknowledge it’s sources and provide links.

 

[merl]

As David said, AI is only as good as the source information, it cant sort out wheat from chaff.
I'm sure a lot of misunderstanding stems from people not understanding the difference between Series and Parallel. You definitely should not connect dissimilar batteries in series, of course this info get's passed around and twisted and before you know it the advice is don't connect dissimilar batteries together AT ALL.
Also dealers and garages aren't going to recommend adding a new battery in parallel with a partially used one because :-
A, they'd be putting their head on the line when something else in the van breaks (Like the TV stops working etc) and the owner immediately thinks "everything was OK until that battery was added" the owners then go to a different dealer and of course the 2nd dealer confirms that the first dealt was a "complete idiot and should never have fitted a new battery onto the existing old one because all sorts of terrible things can happen".
B Much easier and far less risk of A above if they simply say, "we recommend fitting 2 new batteries.
C, They get to sell you 2 new batteries.

I saw one AI article that said that paralleling batteries could lead to overcharging and this could lead to explosions!! What a load of Bull. In order to overcharge a battery you'll need at least 14.6V but probably more like14.8V or more, where on earth is this sort of voltage coming from just by connecting 2 batteries in parallel? It's a joke, and so the myth persists.

I did a quick search on you tube for videos of anyone who's actually tested what really happens (in the real world) when batteries of unequal capacity are connected in parallel and fortunately there's quite a lot of tests. I've linked the first 3 I found below but there's quite a lot, thankfully the recent trend for you tubers to monetise videos with science based information along with Lifepo4 batteries with BMSs that allow monitoring voltage and current and the advent of DC clamp meters shows exactly what DOES happen. Unfortunately the monetisation aspect does lead to videos that are needlessly lengthy but you can always skip the waffle and jump to the end for the summary and results. All are Lifepo4 but the laws of physics don't change for lead acid.

 

[nabsim]

Now I will firstly remind you I forget stuff fairly quickly once I stop using/doing stuff so bear this in mind lol

From my (probably poor) memory I seem to think if I had a bog standard lead acid set up in a van I COULD add a lifepo4 battery to the setup without doing anything else and keeping power in and out connections to the lead battery. I know this is far from an optimal setup by any means but I seem to recall his would work fine and give a much greater power storage capacity.

I will add, if I was thinking of doing this I would research everything again before I did anything. Am I remembering correctly, I think this has to go to David as he has experience with hybrid systems in practice?

 

[merl]

Now I will firstly remind you I forget stuff fairly quickly once I stop using/doing stuff so bear this in mind lol

From my (probably poor) memory I seem to think if I had a bog standard lead acid set up in a van I COULD add a lifepo4 battery to the setup without doing anything else and keeping power in and out connections to the lead battery. I know this is far from an optimal setup by any means but I seem to recall his would work fine and give a much greater power storage capacity.

I will add, if I was thinking of doing this I would research everything again before I did anything. Am I remembering correctly, I think this has to go to David as he has experience with hybrid systems in practice?

Can't really say I want to go down the 'drop in lithium' debate again right now but I think this is generally regarded as the 'go to' device for adding lithium to lead acid.

https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-Li-ion-120-A-EN.pdf

 

[wildebus]

Now I will firstly remind you I forget stuff fairly quickly once I stop using/doing stuff so bear this in mind lol

From my (probably poor) memory I seem to think if I had a bog standard lead acid set up in a van I COULD add a lifepo4 battery to the setup without doing anything else and keeping power in and out connections to the lead battery. I know this is far from an optimal setup by any means but I seem to recall his would work fine and give a much greater power storage capacity.

I will add, if I was thinking of doing this I would research everything again before I did anything. Am I remembering correctly, I think this has to go to David as he has experience with hybrid systems in practice?

I worked on the basic logic of how to combine Lead and Lithium together with an automated way to charge both batteries simultaneously AND independently from the same charger (doing those together may sound strange ) . This was a few years ago and went from theory to test-bed to product creation and release within a few months.
Since I released my VSDR Lithium Controller, unlucky timing meant LiFePO4 battery prices have plummeted even further and for the last 18 months or so I didn't think I would be selling any, but remarkably people are still interested in having Hybrid battery setups. I shipped a VSDR out last week for example and am currently discussing one for install in a Catamaran in France. I've sent them far and wide, including for Yachts in the Aegean Sea and the Adriatic, Off-Grid cabins in North America, Campers in New Zealand and Australia, as well as around Mainland Europe and Scandinavia.
Some people still see the benefit of combining Lead and Lithium is greater than just 100% Lithium on a technical side, not just cost. And not needing Lithium-capable chargers when you use a VSDR is a handy bonus

 

[nabsim]

Can't really say I want to go down the 'drop in lithium' debate again right now but I think this is generally regarded as the 'go to' device for adding lithium to lead acid.

https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-Li-ion-120-A-EN.pdf

Think that's more for use as a split charge relay isn't it? Isn't it one of those Jeff uses?

 

[wildebus]

Think that's more for use as a split charge relay isn't it? Isn't it one of those Jeff uses?

Yup, the Cyrix Li is a voltage sensing relay generally used to connect a Lithium Leisure battery to a Lead Starter Batrtery for charging. The reason these are used rather than a 'normal' VSR is the higher voltage thresholds suitable for Lithium (the normal VSRs and Victrons own Cyrix-ct cannot be used with Lithium). Doesn't actually have any real advantage over a normal D+ controlled relay and doesn't 'fix' the issues with Smart Alternators.
You certainly wouldn't use these to parallel a Leisure Lithium and Leisure Lead.

 

[Exwindsurfer]

Not got a smart alternator David so it doesn't apply to me van is to old for that gobbledegook lolol

 

[wildebus]

Not got a smart alternator David so it doesn't apply to me van is to old for that gobbledegook lolol

Much better without one as well

I fitted the Cyrix-Li to Raes van when he upgraded to Lithium. He has a Smart Alternator and, as we suspected, the Cyrix wouldn't work reliably.
However we used the old workaround of turning on the Headlights if there is a need to charge the Leisure Battery as that makes the Alternator stay on
(however, that workaround doesn't work on vans that also have LED Headlamps)

 

[merl]

You certainly wouldn't use these to parallel a Leisure Lithium and Leisure Lead.

Ah, sorry. I wasn't certain but I knew I'd seen a Victron gizmo that connected between lead and lithium to allow the lithium to charge 'correctly. I'd forgotten about your unit David. Nice BTW, as you say the rapid price drop of lithium must have prevented a lot of sales, having said that if you'd have found yourself making millions those Chinese would have put the cybosh on it with a knock off eventually.

 

[trevskoda]

Yup, the Cyrix Li is a voltage sensing relay generally used to connect a Lithium Leisure battery to a Lead Starter Batrtery for charging. The reason these are used rather than a 'normal' VSR is the higher voltage thresholds suitable for Lithium (the normal VSRs and Victrons own Cyrix-ct cannot be used with Lithium). Doesn't actually have any real advantage over a normal D+ controlled relay and doesn't 'fix' the issues with Smart Alternators.
You certainly wouldn't use these to parallel a Leisure Lithium and Leisure Lead.

Something i was going to ask about but you have helped, cheers..