First… You should only be charging your batteries at 0.9A. Full stop. Break the switch off your charger if you have it.
Second, the chargers should do exactly that, trickle charge the battery. Any “dumb” battery charger you buy should be CC/CV, meaning that it will do 0.9A until it reaches the set voltage (up to 15v), and then back off to as low as 0.05A when it is fully charged. The battery charger I used, the TB6B, had an interesting functionality where it would pulse charge all batteries- it would charge the battery, then stop charging, let the voltage normalize, and then resume charging, about every minute. The battery never got even warm during charging. Might want to give that a try?
Also, if you’re interested in a LiFePO4 battery, just know there aren’t any commercially available ones. Just buy some cells on eBay (the A123 ones are ridiculously awesome), buy a balance charger (TB6B), wire in a balance connector (don’t use a cheap eBay BMS…), and then put a low-voltage cutoff on the output. If you have a Batteries+ nearby, they might have a spot welder and will weld tabs to the batteries if they don’t have them already
Good luck with your battery adventures