Chargers

I tried my 48 Volt LiFePO4 charger on my 48 volt pack and it got it up to 60 plus volts and it was still cranking in some amps. If you want to try I don't think any damage will occur if you monitor charge voltage and not exceed 2.3 v/c. What size battery are you trying to charge? 1.8 amperes is nice for a small pack but shy of proper charging on NPX-80 or larger battery pack. I have to try another LiFePO4 charger that just came back repaired for it gave out day one so I got a V power battery and charger last month or so. Just keep an eye on pack voltage. It is nor like charging a 36 volt pack with 48 or 60 volt charger. Just because it might go into current limit doesn't mean it is safe but 2.3 v/c to 2.35 or 2.4 is not too bad.
Rusty

Here is the charge curve of lithium and SLA.
Lead acid Charge curve

Lithium, LiFePO4 Charge Curve

The I3 V3 process is to make sure the SLA battery full charge. and Lithium do not need this process.
The charge voltage of SLA and Lithium which under same nonimal voltage are different. There maybe occur damage to the battery. Mostly Lithium, lifepo4 charge voltage will be too high for the SLA.