The batteries are Renogy, they recommend 14.4v absorbtion voltage and 13.2v float voltage, elektrobloc ebl 99 manual states that the charge settings for the ebl 99 are 14.3 absorbtion voltage with a charging current of 18A, and 13.8 float voltage
I've spent many hours on the excellent DIY solar forum gleaning very important and technical information, there are some of the most knowledgeable people posting there, some of them involved in the development and production of lifepo4 batteries. There are others there actually running tests on various charge and float voltages and monitoring charge speed and capacity. I've also sought out various technical studies and paid to read the research results. The takeaway bullet points are.
Charging at just 13.6 volts gets the battery up to over 95% charge.
13.8v gets you to 100% but the final couple of percent will take a while because the charge current drops away quickly for the last few percent.
The reason why we charge to over 14v isn't anything to do with actual charging, it's to do with getting the battery voltage to a high enough level that the balance circuitry in the BMS kicks in and balances the cells.
The voltage at which balancing starts varies considerably from BMS to BMS, often it starts at around 13.6v, often nearer 13.7v but there's no guarantee, some BMSs are adjustable within the app.
Upper charge voltage isn't particularly important therefore, it's merely a matter of giving the BMS time to balance the cells.
Some BMS take ages to balance out the cells and are frankly rubbish. So If your battery has particularly mismatched cells and a slow balance time and also needs a high voltage say 13.8v to activate the balance then you really need to let the battery sit at a float voltage higher than the BMS balance trigger threshold and leave it there for a few days. Yes, technically this will damage the cells but it's all about EXTENT because actually the damage will be miniscule.
I've seen a research paper where a lifepo4 battery was charged and floated at
16 volts (in order to accelerate the results) for
2 years 24/7 and it only lost around 25% capacity (could have been 30% can't recall) so a couple of days floating at 13.8v isn't going to be significant.
So My personal knowledge on lifepo4 is.....
Charge voltage isn't really important as long as you go over 13.8v
Float voltage isn't really important. BUT
Don't leave them floating for weeks and weeks on end.
Done.
Virtually any lead acid charger will fit the above requirements including your existing but there's a couple of things to consider.
When charging a LFP battery instead of a lead acid the charger will probably spend more time in bulk mode delivering it's full amperage, this means the charger will be working at full tilt for longer than usual. Theoretically the electronics will be OK because the design is ultimately rated for it's specified current but if the the charger has a maximum AH rating then it's probably best to limit that to 50% with LFP, so if your charger has a maximum AH of 200Ah with lead acid then don't go above a 100Ah lithium. If there's no max Ah rating then the charger is probably continuously rated and theoretically you can connect anything to it.
Watch out for standard blade fuses carrying over 15A, they can get hot and melt especially as the current being carried gets close to the fuse's value, this is particularly important when charging LFP with an existing lead acid charger because as mentioned the charger's full current delivery could go on for longer meaning more heat developing.
