Chargers again vary and some are better for your battery than others. You can pick up a cheap from supercheap or get a Guest/ C-Tek/Minn Kota. These are multistage chargers and you can set and forget them once you put them on.
For 100amp battery, if you want to charge up overnight then at minimum a 5amp charger
I have a 105 Amp/hr lead-acid battery with a C-Tek 7000 charger, and hope to have the battery for a long time.
Norm
P.S. I have a 32V 3A charger if anyone is interested, was used for electric bike battery.