I would like to ask if the components in D5, D6, D7, and M1 in DC2044A can be omitted. I just want to use LTC4020 for lead-acid charging. In the back I will add a battery and switching power supply to switch LTC4418 to switch. .
Diodes D5 and D6 are optional. See the discussion in the datasheet, p. 24-25, section named Optional Schottky Diode (Db, Dd) Selection. I recommend including D6.
Diode D7 is also optional. See the discussion in the datasheet, p. 25, section named INTVCC LDO Output, and BST1 and BST2 Supplies. (last sentence).
Depending on your application, you may want to include D5-D7. I recommend you leave a place for them in the PCB, so you will be able to add them in they are needed.
M1 is not necessary for lead-acid applications if you do not require the instant-on function. Please refer to the datasheet, p. 27-28, section named PowerPath FET Function and Instant-On.