I have a dual battery system in the trok that has been servicing me well for years.
The last auxiliary battery which has now died on me after about 5-6years is a 150Ah Royal VRLA
I’m thinking of going the lithium route and is looking for a drop in replacement type. It would be nice to have those amp hours again but obviously not crucial because a smaller lithium will give me the same hours due to the better DOD I can take it to.
Thing is, I don’t necessary want to replace my dc2dc charger (a Ctek D250S which is also an MPPT capable of doing 20 amps - but has no lithium charging profile)
So from what I’ve read, this is not crucial, as long as the charger as able to step up the volts to about 14,4 which is what the lithiums require (and my Ctek does beautifully), and it should not trickle charge or float the battery - which lithiums don’t appreciate.
Is this correct? And if I find a suitable drop in replacement, do I still need a BMS where it is only one battery?
Your thoughts on the matter is most welcome and appreciated please.
The point of a “drop in” replacement is that you can use the existing charger. I would not be concerned with so-called trickle-charging. All it means is that it holds the battery at a voltage lower than absorb, but high enough to prevent self-discharge (in a lead acid). This is generally something like 13.8V or 13.5. Sometimes the charger will have a profile for gel/agm batteries that uses 13.5V. This is perfectly good for a 4-cell battery, and equates to somewhere between 3.4 and 3.45V per cell.
Drop-in replacements should already have a built-in balancer and protection circuit.
The manual doesn’t give the specific bulk and floating data.
All I could find is that given on pages 12 & 13 but I think I should be ok.
Now to just find a drop in replacement. It is a rather large battery (kinda like a truck battery with both poles on the one side) Wonder what the odds are of finding something in this size so it can fit into the specific spot in the load bin.
BlueNova makes a good one. I see there is also a Mecer-branded unit for about half price.
Of course, since it is a LFP battery that can handle deeper discharge, you may well go for a 100Ah instead. Sustainable has one for 8k right now (they are usually not the cheapest but this one looks good).
Just glad to hear there are lithium alternatives for this monster I have. I might even go for the big one, especially if it is identical in physical dimensions and pole location so I could literally just drop it into place.
Not at all interested in going lead acid again. But I also don’t think its necessary to upgrade my Ctek to the newer model that is geared for lithium charging.
So my cost will only be a lithium battery and some fiddling with the existing wiring to make it reach where it should. If I go down to 100-108Ah batteries, the poles are on opposite sides of the batteries.
Currently the poles are both on the same side.
I’d rather pay someone to make me something with 2nd hand cells. which will fit where it must. I’m getting tired of fiddling.
I am not outdoorsy but I am curious so I looked around the internet a bit. I suspect the D250S will be able to cope with a LiFePO4 to some extent but you will need to deffinitely double check some things and do some trial runs before venturing into the wild.
The BMS that makes the lithium magically “drop in replacement” can possibly do other things that will probably at least be inconvenient at times when used in a non-lithium option type setup.
The CTek seems to be fully automatic and includes a first desulphation phase which apparently can go go up to 15.8V → from what I can see batteries like the Bluenova drop-ins have a BMS that will disconnect at 15.6V.
You could face a similar problem if it is quite cold because the CTek does auto temperature compensation (since it does not know there is a lithium connected it could try and charge the battery at a too high voltage again causing the BMS to disconnect).
Also if you have a setup that make the “decision” to charge purely on voltage you could find that if u had a fairly light load during the night and the voltage did not lower much (remembering that LiFePO4 has a fairly flat voltage discharge curve) that the battery may not be charged.
If you ever discharge the battery so low that the BMS disconnects you could find that the CTek might not be able to get the battery out of this safety state because the charger sees nothing connected to it so will not provide charge and charge is what is required to get the BMS to close its inputs again.
BTW, if you currently have a battery with post connections, most drop in replacements bigger than 50Ah have a threaded connection terminal so you may need to at least change your existing connection lugs.
Last thing, since it does not look like they make it clear - unless something has changed the Mecer 200Ah makes use of 2nd Life Cells
Village Idiot, very valuable points to ponder thank you.
The flat voltage curve is actually of most concern. In other words the Ctek potentially wont see the battery as needing a charge until it is really and properly flat. Don’t know if the Ctek works on volts to determine this. This could really throw a spanner in the works. I think I must email Ctek to get this info.
As for it being drained to low so that the BMS disconnects it, I have a solution for this. My 1st dual battery system is still in place which comes directly from the alternator. I could use this to “jump start” the battery and have the BMS connect again.
I have those poles that screw on to threaded terminals so I could use both.
Yes, almost all the places I shopped at states that it is 2nd life cells so I’m aware of that.
What’s the bulk setting of the CTEK, I used one a couple years ago and can’t quite remember whether it’s 14.4 or
My major concern will be the max charge voltage of the CTEK, whether it can / will ever go over the voltage the lithium batteries BMS can handle.
I have a few small Blue Nova 22 Ah lithiums in use which I charge with a Benton BX2, 7 A charger, the charger isn’t officially lithium compatible. In the normal AGM charging mode it charges at a max of 14.4v and the Blue Nova bulk setting should be at 14.4v, so I figured it will be ok and have been using it like that for months now.
Look at the Freedom Won 12V drop in replacement range as well, on paper the Freedom Won 100 Ah looks better to me than the Blue Nova 108 Ah, C ratings and such, the pricing is also very similar.