Lithium Parallel In Harmony With Lead Acid

BatteryMegaUK

BatteryMegaUK

Trader (Batteries)
Joined
Jun 20, 2019
Posts
44
Likes collected
106
Funster No
61,793
MH
Don't own one yet
Exp
Battery Expert
Good Afternoon Funsters,

We decided to run a test in house to prove that you can run a lead acid battery in parallel with a lithium battery. The results from our tests indicate that it doesn’t make a difference if there is a lead acid battery either wired in parallel or connected as an engine starting battery.

This shows that you don’t necessarily need to wait for your lead acid to fail before replacing it with lithium or worry about the fact your engine starting battery is lead acid which we know some people are. We also charged these on both the standard lead acid setting and on the lithium setting - the only difference unsurprisingly was a slightly longer recharge time.

If you have any battery related questions please ask away!

Battery Megastore.
 

Attachments

  • TN Lithium Parallel.jpg
    TN Lithium Parallel.jpg
    131.3 KB · Views: 190
Hi, can you tell us how you tested this? for instance how many charge discharge cycles over what period of time and the condition of each battery at the end of the test. I think people investing in expensive lithium batteries would want to know they are not shortening the life of the battery by using an incorrect charging regime.
 
And perhaps what you set the charger to given LiPo requirements are very different to LA ?
 
Or better still.... What guarantee will you give to your research and advise.
If someone destroys their lithium battery or Flooded battery after taking your advise will you replace it even if you didn't supply it?
 
Jaws said:
And perhaps what you set the charger to given LiPo requirements are very different to LA ?
Click to expand...
It's not a LiPo (Lithium polymer) It is a LiFE (Lithium Iron Phosphate) COMPLETELY DIFFERENT..

Subscribers  do not see these advertisements

 
I'm not up to date with lithium leisure batteries. Still too expensive for me.
You can connect a GEL and Lead acid battery but the GEL's life with be short lived as they require a different charge rate and a longer charge to lead acid. If I were you I would read up on it a bit more. Or phone Alpha Batteries and ask them what they think. I would hate to see you destroy an expensive lithium battery. You can connect any batteries together but they might not last long if the have different charge and discharge rates. Plus it can work out expensive if they catch fire in your MH.
 
Nominal LiFe voltage (per cell) 3.2v..... 4 cells grouped give you 12.8V
Nominal Lead Acid v (per cell) 2.1v... 6 cells grouped give you 12.6v
This is why you can connect them to a lead acid without issue.
At the very worst, your lead acid charger will not fully charge the LiFe battery... which is actually BETTER for the LiFe battery as it is at the ENDS of the usable voltage scale which degrade the battery quicker!
 
Jim said:
Andy no need for the capitals... given the thread, we all know he meant LiFePO4
Click to expand...
Terminology is quite important when the subject can be so confusing for some people. It needs straightening out more so more people understand the differences.
 
Jim said:
Andy no need for the capitals... given the thread, we all know he meant LiFePO4
Click to expand...
Unless you study the attached photo you don't.
Nowhere in the text does it say anything other than Lithium.

Subscribers  do not see these advertisements

 
Which proves my point... (sorry Pappa)

No one in their right mind would put a LiPo in a MH and try and charge it with a lead acid charger... well not unless you want a big fire and to claim on the insurance that is :D
 
Another note to add is that the Maximum charge (per cell) for a LiFe is 3.65v... 4 cells Grouped gives you. 14.6v, so EVEN if you had an old school charger and it got left on it's one and only setting of 14.2 -14.4 v the LiFe battery would be in better shape than the lead acid would be if left for an extended period . :D
 
I can think of a number of issues with this. But the one that would concern me the most is...
As a Pb battery discharges it's voltage falls. Whereas a Li battery will maintain an almost constant voltage across the bulk of it's discharge range.
As the Pb battery voltage lowers the Li battery will then start charging the Pb battery. This is wasteful as it is not efficient to charge Pb battery at all.
The other possibility is that as the Li battery has a higher voltage it will provide more power and go through it's full discharge cycle long before the Pb battery reaches 60%.

I am never happy mixing manufacturers or age, never mind chemistry.

Yes it might work, but in my opinion it is far far from advisable...
 
Last edited:
It does have a couple of advantages while you are in transition to a full lithium setup though, I don't think it's a great idea long term either, but for those not wanting to drop a grand on two TN's right out out of the bag, it is a good (and safe) stepping stone.

It might actually make the lead acid last longer as it will keep it topped up.
The LiFe will charge faster than the Lead acid for any given input.
You'd probably most likely just be using the capacity of the LiFe in most cases.
If you did draw any large currents from your battery bank, instead of the voltage sagging to a level that may damage the lead acid, the LiFe would support the load better, again lengthening the life of the lead acid..
 
Last edited:
pappajohn said:
Unless you study the attached photo you don't.
Nowhere in the text does it say anything other than Lithium.
Click to expand...

So not everyone then John, just you that doesn't realise we're talking about LiFePO4 batteries when we say 'Lithum' . :D

Subscribers  do not see these advertisements

 
I would also worry that the Pb voltage might confuse the LiFePO4 battery management system. Would cell monitoring and cell balancing be compromised?
 
i just go to the scrap yard when i want a battery the leisure battery i have at the moment cost me £15 and has lasted me two years and cam of a scania truck it a big one when i way it in when its done i will probably get £15 for it :wink: the last one lasted three years
bill
 
Wildbill said:
i just go to the scrap yard when i want a battery the leisure battery i have at the moment cost me £15 and has lasted me two years and cam of a scania truck it a big one when i way it in when its done i will probably get £15 for it :wink: the last one lasted three years
bill
Click to expand...
Bill, I thought Scania trucks were 24 volt
Am I out of date?
Phil
 
Clear something up please. In the average (older) Motorhome setup, it is only the charging phase that has all the batteries connected (by whatever means)?. Therefore under load conditions (discharging) the Chassis Battery should be unaffected? Otherwise, one could be in a situation where the vehicle will not have sufficient capacity to start?. Any true BtoB charge system the flow would be determined by the monitoring "software" with the intention of compensating for "Ghost" drains, E.g. Clocks and other background drains.
 
Jim said:
So not everyone then John, just you that doesn't realise we're talking about LiFePO4 batteries when we say 'Lithum' . :D
Click to expand...
Er, not just Papa ... I haven't done a lot of looking into Lithium batteries so I wouldn't necessarily know the difference and I've been on the forum a long time and seen them mentioned occasionally, for a newbie it could be confusing/misleading so when stuff like this is mentioned IMV it shoudl state clearly exactly WHAT is being discussed.

Could I suggest that you amend the title to show it is referring specifically to LifePO4 batteries.
 
Minxy Girl said:
clearly exactly WHAT is being discussed.
Click to expand...

If you are worried about someone making a mistake then use the full technical name if you wish. But I'll just refer to them as lithium :)

Subscribers  do not see these advertisements

 

Join us or log in to post a reply.

To join in you must be a member of MotorhomeFun

Join MotorhomeFun

Join us, it quick and easy!

Join us

Log in

Already a member? Log in here.

Latest journal entries

Back
Top